test: create new test architecture with shared property/API tests

- Add tests/common/ with parametrized property tests (positivity, shape, NaN, stability)
- Add tests/physics/ with unique physics behavior tests for 6 correction components
- Add tests/quality/ with API contract tests for 6 correction components
- Add pytest markers in pyproject.toml: property, physics, api, quality, integration
- New tests: 94 tests passing (physics + quality + common helpers)
- Old tests in tests/ root still present — migration in progress
- Total: 261 tests collected (230 old + 94 new - 63 duplicates removed)

The shared helpers eliminate 18 duplicate test patterns across correction
components. Each component now has:
  - tests/physics/test_<name>.py — unique physics behavior
  - tests/quality/test_api_<name>.py — API contract + shared property checks
  - tests/common/test_property_tests.py — shared helpers (imported, not duplicated)

pyproject.toml

@@ -49,6 +49,15 @@ line-length = 88
 
 [tool.pytest.ini_options]
 testpaths = ["tests", "notebooks"]
+markers = [
+    "property: Physics property tests (positivity, monotonicity, limits)",
+    "physics: Physics behavior tests (energy dependence, Z dependence)",
+    "api: API contract tests (signatures, return types, error handling)",
+    "quality: Code quality tests (shape, type, NaN, stability)",
+    "integration: Full pipeline integration tests",
+    "slow: Tests that take >1s to run",
+    "requires_ensdf: Tests requiring paceENSDF package",
+]
 
 [tool.ruff]
 line-length = 88