Add 13 new procedural datasets across 7 categories

New dataset categories: combinatorics, statistics, optimization, and
formal languages. Extended existing algebra, arithmetic, probability,
logic, and graphs packages with complex_advanced, linear_algebra, limits,
number_theory, conditional_probability, set_operations, and job_scheduling.

Each dataset includes config validation, deterministic seeding, custom
scoring, curriculum support, and comprehensive unit tests (92 new tests).

tests/test_combinatorics.py

@@ -0,0 +1,76 @@
+import pytest
+
+from reasoning_gym.combinatorics.combinatorics import (
+    CombinatoricsConfig,
+    CombinatoricsCurriculum,
+    CombinatoricsDataset,
+)
+
+
+def test_config_validation():
+    with pytest.raises(AssertionError):
+        config = CombinatoricsConfig(min_n=1)
+        config.validate()
+
+    with pytest.raises(AssertionError):
+        config = CombinatoricsConfig(min_n=10, max_n=5)
+        config.validate()
+
+
+def test_deterministic():
+    config = CombinatoricsConfig(seed=42, size=10)
+    ds1 = CombinatoricsDataset(config)
+    ds2 = CombinatoricsDataset(config)
+    for i in range(len(ds1)):
+        assert ds1[i] == ds2[i]
+
+
+def test_item_structure():
+    config = CombinatoricsConfig(seed=42, size=50)
+    ds = CombinatoricsDataset(config)
+    for i in range(len(ds)):
+        item = ds[i]
+        assert isinstance(item, dict)
+        assert "question" in item
+        assert "answer" in item
+        assert "metadata" in item
+        assert item["metadata"]["source_dataset"] == "combinatorics"
+
+
+def test_answer_correctness():
+    config = CombinatoricsConfig(seed=42, size=100)
+    ds = CombinatoricsDataset(config)
+    for i in range(len(ds)):
+        item = ds[i]
+        answer = item["answer"]
+        assert answer.lstrip("-").isdigit(), f"Item {i}: answer '{answer}' is not an integer"
+
+
+def test_score_wrong_answer():
+    config = CombinatoricsConfig(seed=42, size=10)
+    ds = CombinatoricsDataset(config)
+    item = ds[0]
+    score = ds.score_answer(item["answer"], item)
+    assert score == 1.0
+
+
+def test_curriculum():
+    curriculum = CombinatoricsCurriculum()
+    base_value = {"size": 50, "seed": 1}
+    base_cfg = curriculum.generate_configuration(base_value)
+    assert base_cfg.seed == 1
+
+    curriculum.increment_attr_level("n_range")
+    increased_cfg = curriculum.generate_configuration(base_value)
+    assert increased_cfg.max_n >= base_cfg.max_n
+
+
+def test_task_types():
+    for task_type in ("ncr", "npr", "permutations_repetition", "inclusion_exclusion", "stars_and_bars", "pigeonhole"):
+        config = CombinatoricsConfig(
+            seed=42, size=10, task_types=(task_type,), task_weights=[1.0]
+        )
+        ds = CombinatoricsDataset(config)
+        for i in range(len(ds)):
+            item = ds[i]
+            assert item["metadata"]["task_type"] == task_type