Validate scorer thresholds in process_py

[gaoflow]

Summary

process_cpp validates score_cutoff and score_hint against the scorer's declared result range, while process_py silently accepts invalid values. This affects all five public process entry points: extractOne, extract, extract_iter, cdist, and cpdist. It is the process-layer divergence noted in #488.

Changes

• Validate built-in scorer cutoffs and hints from their _RF_ScorerPy flags while leaving custom scorers unchanged.
• Mirror the C++ conversions for float32 and size_t, including boundary rounding and exception behavior.
• Cover both backends, all five APIs, upper/lower range errors, cutoff/hint, normalized and integer scorers, and conversion edge cases.

Testing

• python -m pytest tests (507 passed)
• black --check src/rapidfuzz/process_py.py tests/test_process.py
• ruff check src/rapidfuzz/process_py.py tests/test_process.py
• python tools/test_scorer_typing.py
• python -m mypy tools/test_process_typing.py --warn-unused-ignores
• python -m pyright -p tools/pyrightconfig.json tools/test_process_typing.py
• Differential matrix: 300 backend/API/type/boundary combinations, no differences.