Add pre-commit lint hooks: cast, private functions, partial assertions

[hiroshinishio]

Summary

• Added 3 new pre-commit lint hooks enforcing coding standards automatically:
  • check_cast_usage.sh: Blocks cast() in implementation files (allowed in test fixtures)
  • check_private_functions.sh: Blocks _-prefixed function definitions in impl files (inline or own file)
  • check_partial_assertions.sh: Blocks assert X in Y in test files (use assert X == Y)
• Updated check_test_files.sh to skip comment-only diffs (no test change required for adding/removing comments)
• Excluded test files from ruff T201 print check (print in tests is fine)
• Updated CLAUDE.md testing guidance: running impl to get output is OK, but must manually verify correctness
• Skipped integration tests by default via pytest.ini -m "not integration" to cut 236s from pre-commit

Social Media Post (GitAuto)

Add pre-commit hooks enforcing code quality rules

• New hooks block cast() in impl files, private functions, and partial test assertions
• Integration tests now skipped by default, cutting pre-commit time by over 3 minutes
• Comment-only diffs no longer require test file changes

Social Media Post (Wes)

Three rules I kept repeating in code reviews: no cast in production code, no private functions, no partial assertions. Wrote shell scripts to enforce all three at commit time. Now I review logic instead of style.