Code quality improvements: modernize string formatting and fix linting issues

[Carreau]

(because pre-commit autoupdate fails and can't fix the various cases)

This PR modernizes the codebase by replacing older string formatting patterns with f-strings, fixes deprecated logging constants, improves exception handling, and addresses various linting issues.

Key Changes

• String formatting modernization: Replaced .join() calls and string concatenation with f-strings in:

  • traitlets/traitlets.py: _resolve_string() method
  • traitlets/config/application.py: flatten_flags() method
  • traitlets/utils/text.py: _dedent() function

• Logging constant updates: Replaced deprecated logging.WARN with logging.WARNING throughout:

  • traitlets/config/application.py: Updated LevelFormatter.highlevel_limit and log_level default value
  • tests/config/test_application.py: Updated test assertions
  • tests/test_typing.py: Updated typing test

• Exception handling improvements:

  • traitlets/traitlets.py: Changed bare raise e to bare raise for cleaner exception re-raising
  • traitlets/config/application.py: Changed AssertionError to TypeError for invalid subcommand mappings (more semantically correct)

• Type annotation ordering: Normalized union type ordering to follow a consistent pattern (e.g., Sentinel | str | None instead of Sentinel | None | str)

• Linting improvements:

  • Removed unnecessary # noqa: E741 comments for variable names l (now using ruff which doesn't flag this)
  • Added appropriate # noqa comments for intentional patterns (e.g., TRY203 for SystemExit handling, LOG001 for logger instantiation)
  • Removed redundant # noqa: F405 comment from __all__ export
  • Updated pyproject.toml to ignore BLE001 for defensive exception handling

• Tooling: Updated ruff pre-commit hook from v0.15.22 to v0.16.1

Implementation Details

The changes maintain backward compatibility while improving code quality and readability. The exception handling change from raise e to bare raise preserves the original traceback, which is the Python best practice. Type annotation reordering follows PEP 604 conventions for consistency.

[codecov]

Codecov Report

❌ Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.96%. Comparing base (626bbe5) to head (5eeed47).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
traitlets/config/application.py	75.00%	1 Missing ⚠️

Components	Coverage Δ
traitlets	85.30% <88.88%> (-0.06%)	⬇️
tests	99.03% <100.00%> (ø)

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