feat: .at_most(n) quantifier closes the symmetry gap with at_least/exactly/between (#265)

Adds `.at_most(n)` on both `RegexBuilder`/`Pattern` and as an
`at_most(n, operand)` factory. Closes the symmetry gap in the quantifier
lineup — we had `exactly(n)`, `at_least(n)`, and `between(lo, hi)`, but
no `{0,n}` shorthand.

## What is new
- `AtMostElement(times, child)` in the elements union, rendered as
`{0,times}` by the quantifier suffix dispatch.
- `.at_most(count)` chain method on `QuantifiersMixin` — validates
`count > 0` (matches the `at_least` contract).
- `at_most(count, operand)` free-function factory in the humre-style
API.
- Re-exported through `edify.pattern` and top-level `edify`.

## Example
```python
from edify import DIGIT, at_most, Pattern

at_most(3, DIGIT).to_regex_string()             # \d{0,3}
Pattern().at_most(3).digit().to_regex_string()  # \d{0,3}
```

Closes #130

3 files changed, 25 insertions, 0 deletions

diff --git a/tests/builder/builder.test.py b/tests/builder/builder.test.py
index 062e1ae..33aa17d 100644
--- a/tests/builder/builder.test.py
+++ b/tests/builder/builder.test.py
@@ -348,6 +348,12 @@ def test_at_least():
     regex_compilation("\\w{3,}", expr)
 
 
+def test_at_most():
+    expr = RegexBuilder().at_most(3).word()
+    regex_equality("\\w{0,3}", expr)
+    regex_compilation("\\w{0,3}", expr)
+
+
 def test_between():
     expr = RegexBuilder().between(3, 5).word()
     regex_equality("\\w{3,5}", expr)
diff --git a/tests/builder/validation.test.py b/tests/builder/validation.test.py
index e4898ad..53128c5 100644
--- a/tests/builder/validation.test.py
+++ b/tests/builder/validation.test.py
@@ -109,6 +109,11 @@ def test_at_least_non_positive_raises():
         RegexBuilder().at_least(-1).digit()
 
 
+def test_at_most_non_positive_raises():
+    with pytest.raises(MustBePositiveIntegerError):
+        RegexBuilder().at_most(0).digit()
+
+
 def test_between_negative_lower_raises():
     with pytest.raises(MustBeIntegerGreaterThanZeroError):
         RegexBuilder().between(-1, 5).digit()
diff --git a/tests/pattern/factories/quantifiers.test.py b/tests/pattern/factories/quantifiers.test.py
index 8a6f34f..a0f558a 100644
--- a/tests/pattern/factories/quantifiers.test.py
+++ b/tests/pattern/factories/quantifiers.test.py
@@ -7,6 +7,7 @@ from edify import (
     WORD,
     Pattern,
     at_least,
+    at_most,
     between,
     between_lazy,
     char,
@@ -62,6 +63,14 @@ def test_at_least_produces_open_ended_quantifier():
     assert at_least(2, DIGIT).to_regex_string() == "\\d{2,}"
 
 
+def test_at_most_produces_zero_lower_bound_quantifier():
+    assert at_most(3, DIGIT).to_regex_string() == "\\d{0,3}"
+
+
+def test_at_most_groups_a_multi_element_operand():
+    assert at_most(3, DIGIT + WORD).to_regex_string() == "(?:\\d\\w){0,3}"
+
+
 def test_between_produces_greedy_bounded_quantifier():
     assert between(2, 4, DIGIT).to_regex_string() == "\\d{2,4}"
 
@@ -84,6 +93,11 @@ def test_at_least_rejects_negative_count():
         at_least(-1, DIGIT)
 
 
+def test_at_most_rejects_zero_count():
+    with pytest.raises(MustBePositiveIntegerError):
+        at_most(0, DIGIT)
+
+
 def test_between_rejects_negative_lower_bound():
     with pytest.raises(MustBeIntegerGreaterThanZeroError):
         between(-1, 5, DIGIT)