chore!: package reorg + uv/ruff/pytest/hatchling toolchain + Python 3.11 floor (#255)

## Summary

Closes #68 — package reorganization to a single-purpose, dir-per-concern
layout (no `src/`).
Closes #69 — toolchain migration to `uv` + `ruff` + `pytest` +
`hatchling` + `hatch-vcs`, driven entirely from `pyproject.toml`.
Closes #253.
Closes #259 — drop `.editorconfig`; LF / trim / final-newline / Python
indent now enforced by `mixed-line-ending` (added in fixup) + existing
pre-commit hooks + `ruff format`.— Python floor bump to 3.11; drops
`py39` / `py310` / `pypy310` from the CI matrix.

The three issues are paired by construction (dropping `src/` requires
the new build backend's package discovery, and the 3.11 floor lets the
new layout use `typing.Self`, frozen dataclasses, `match`/`case`, and
Python-3.11 idioms throughout).

## Highlights

**Layout** — `edify/builder/` (RegexBuilder + 11 mixin files + `types/`
for state/flags/frame/protocol), `edify/elements/types/` (sealed
dataclass union: 16 leaves, 7 char-shaped, 4 captures, 7 groups, 9
quantifiers, RootElement), `edify/compile/` (per-family render functions
+ dispatch, plus `quantifier/` subpackage for suffix + apply),
`edify/validate/`, `edify/errors/` (typed exception hierarchy),
`edify/library/` (per-validator files in family folders: `email/`,
`ip/`, `date/`, plus flat single-validator files), `pattern/`,
`serialize/`, `result/` skeletons.

**Toolchain** — replaces `tox` / `virtualenv` / `flake8` / `isort` /
`black` / `setup.py` / `setup.cfg` / `pytest.ini` / `.coveragerc` /
`.bumpversion.cfg` / `MANIFEST.in` / `ci/` / `tests.local.sh` with
`pyproject.toml`-driven `uv` + `ruff` + `pytest` + `hatchling` +
`hatch-vcs`. CI workflow rewritten to `uv sync --frozen` + `uv run
pytest`; required-status-check names preserved (`check`, `docs`, `py311
(ubuntu)`, `py312 (ubuntu)`, `py313 (ubuntu)`, `py314 (ubuntu)`,
`pypy311 (ubuntu)`). Pre-commit replaced with `ruff` hooks, all hook
repos pinned by commit SHA.

**Tests** — reorganised under `tests/builder/` and
`tests/library/<family>/` using the `*.test.py` naming shape. 173 tests,
100% line coverage, ruff lint + format clean, `uv build` produces sdist
+ wheel cleanly.

## Behaviour changes versus 0.3

These will get their own upgrade-guide entries when the migration
tooling lands (#80):

- `to_regex_string()` now returns the bare pattern (no `/.../` wrap).
- `to_regex()` on a named back-reference compiles successfully via
`(?P=name)` instead of raising.
- Builder errors raise typed `EdifyError` subclasses
(`MustBeAStringError`, `StartInputAlreadyDefinedError`, etc.) instead of
bare `Exception` — catch via `except EdifyError`.
- Internal helpers (`apply_quantifier`, `frame_creating_element`,
`evaluate`, `state`, etc.) removed outright per the 0.3 → 1.0 stub-free
policy.

1 files changed, 153 insertions, 0 deletions

diff --git a/tests/errors/errors.test.py b/tests/errors/errors.test.py
new file mode 100644
index 0000000..12cfcd5
--- /dev/null
+++ b/tests/errors/errors.test.py
@@ -0,0 +1,153 @@
+from edify.errors.anchors import (
+    CannotDefineStartAfterEndError,
+    EndInputAlreadyDefinedError,
+    StartInputAlreadyDefinedError,
+)
+from edify.errors.captures import InvalidTotalCaptureGroupsIndexError
+from edify.errors.input import (
+    MustBeAStringError,
+    MustBeInstanceError,
+    MustBeIntegerGreaterThanZeroError,
+    MustBeLessThanError,
+    MustBeOneCharacterError,
+    MustBePositiveIntegerError,
+    MustBeSingleCharacterError,
+    MustHaveASmallerValueError,
+)
+from edify.errors.internal import (
+    FailedToCompileRegexError,
+    NonFusableElementError,
+    UnexpectedFrameTypeError,
+    UnknownElementTypeError,
+)
+from edify.errors.naming import (
+    CannotCreateDuplicateNamedGroupError,
+    NamedGroupDoesNotExistError,
+    NameNotValidError,
+)
+from edify.errors.structure import (
+    CannotCallSubexpressionError,
+    CannotEndWhileBuildingRootExpressionError,
+)
+
+
+def test_start_input_already_defined_outside_subexpression():
+    error = StartInputAlreadyDefinedError()
+    assert "already has a start" in str(error)
+    assert "ignore_start_and_end" not in str(error)
+
+
+def test_start_input_already_defined_in_subexpression():
+    error = StartInputAlreadyDefinedError(in_subexpression=True)
+    assert "ignore_start_and_end" in str(error)
+
+
+def test_end_input_already_defined_outside_subexpression():
+    error = EndInputAlreadyDefinedError()
+    assert "already has an end" in str(error)
+    assert "ignore_start_and_end" not in str(error)
+
+
+def test_end_input_already_defined_in_subexpression():
+    error = EndInputAlreadyDefinedError(in_subexpression=True)
+    assert "ignore_start_and_end" in str(error)
+
+
+def test_cannot_define_start_after_end():
+    error = CannotDefineStartAfterEndError()
+    assert "start of input after defining an end" in str(error)
+
+
+def test_invalid_total_capture_groups_index():
+    error = InvalidTotalCaptureGroupsIndexError(5, 3)
+    assert "Invalid index #5" in str(error)
+    assert "only 3 capture groups" in str(error)
+
+
+def test_must_be_a_string():
+    error = MustBeAStringError("Name", "int")
+    assert "Name must be a string" in str(error)
+    assert "int" in str(error)
+
+
+def test_must_be_one_character():
+    error = MustBeOneCharacterError("Value")
+    assert "Value must be one character long" in str(error)
+
+
+def test_must_be_single_character():
+    error = MustBeSingleCharacterError("Value", "str")
+    assert "Value must be a single character" in str(error)
+    assert "str" in str(error)
+
+
+def test_must_be_positive_integer():
+    error = MustBePositiveIntegerError("count")
+    assert "count must be a positive integer" in str(error)
+
+
+def test_must_be_integer_greater_than_zero():
+    error = MustBeIntegerGreaterThanZeroError("x")
+    assert "x must be an integer greater than zero" in str(error)
+
+
+def test_must_be_instance():
+    error = MustBeInstanceError("Expression", "str", "RegexBuilder")
+    assert "Expression must be an instance of RegexBuilder" in str(error)
+    assert "str" in str(error)
+
+
+def test_must_have_a_smaller_value():
+    error = MustHaveASmallerValueError("z", "a")
+    assert "z must have a smaller character value than a" in str(error)
+
+
+def test_must_be_less_than():
+    error = MustBeLessThanError("X", "Y")
+    assert "X must be less than Y" in str(error)
+
+
+def test_name_not_valid():
+    error = NameNotValidError("bad name")
+    assert "Name bad name is not valid" in str(error)
+
+
+def test_cannot_create_duplicate_named_group():
+    error = CannotCreateDuplicateNamedGroupError("dup")
+    assert 'Can not create duplicate named group "dup"' in str(error)
+
+
+def test_named_group_does_not_exist():
+    error = NamedGroupDoesNotExistError("missing")
+    assert 'Named group "missing" does not exist' in str(error)
+
+
+def test_cannot_end_while_building_root_expression():
+    error = CannotEndWhileBuildingRootExpressionError()
+    assert "Can not end while building the root expression" in str(error)
+
+
+def test_cannot_call_subexpression():
+    error = CannotCallSubexpressionError("capture")
+    assert "Can not call subexpression" in str(error)
+    assert "capture" in str(error)
+
+
+def test_unknown_element_type():
+    error = UnknownElementTypeError("WeirdElement")
+    assert "WeirdElement" in str(error)
+
+
+def test_non_fusable_element():
+    error = NonFusableElementError("DigitElement")
+    assert "Cannot fuse element of type DigitElement" in str(error)
+
+
+def test_unexpected_frame_type():
+    error = UnexpectedFrameTypeError("DigitElement")
+    assert "Stack frame anchored at unexpected element type DigitElement" in str(error)
+
+
+def test_failed_to_compile_regex():
+    error = FailedToCompileRegexError("missing )")
+    assert "Cannot compile regex: missing )" in str(error)