[pep8-naming] Flag variables bound in match patterns (N806/N815/N816)

[gopoto]

Summary

Extend pep8-naming to catch mixed‑case identifiers introduced via structural
pattern matching:

• N806: variables bound by a match pattern inside functions
• N815: variables bound by a match pattern inside classes
• N816: variables bound by a match pattern at module scope

Previously these names were ignored since they weren’t visited during
expression store analysis. Add a pattern walker that binds pattern names and
runs the same naming checks based on the current scope. Test fixtures and
snapshots for N806, N815 and N816 have been updated with match cases.

Test Plan

Run Ruff against the pep8_naming fixtures:

cargo run -p ruff -- check crates/ruff_linter/resources/test/fixtures/pep8_naming/N806.py --select N806 --no-cache

The added pattern variables are now flagged. All unit and integration tests pass
after updating the affected snapshots:

cargo clippy --workspace --all-targets --all-features -- -D warnings
RUFF_UPDATE_SCHEMA=1 cargo test
uvx pre-commit run --all-files --show-diff-on-failure

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This PR was generated by an AI system in collaboration with maintainers: @carljm, @ntBre

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.