ci: restore deterministic Ruff gate

[AIwork4me]

Summary

• pin Ruff so local and GitHub Actions use the same lint semantics
• make the repository lint rule set explicit instead of depending on evolving defaults
• fix selected lint findings with behavior-preserving changes
• preserve deliberate fault-containment and cross-platform behavior

Why

The core CI job was failing at ruff check ., while tests and the platform-contract job were passing.

The previous development dependency allowed a floating Ruff version, so the effective lint gate changed between Ruff 0.15.19 on the existing developer environment and Ruff 0.16.2 on a fresh GitHub runner.

This PR makes that gate deterministic and restores a clean CI baseline without weakening benchmark or runtime guarantees.

Safety

This PR does not change:

• benchmark scores
• model revisions
• inference configuration
• scoring configuration
• Hardware Matrix evidence
• ROCmDoc trust status

Behavior-sensitive findings were reviewed manually rather than globally auto-fixed. Broad exception handlers, retry behavior, lock acquisition/release, subprocess behavior, and backend behavior are unchanged.

Validation

• Ruff: 0.16.2 — PASS
• pytest: 176 passed, 1 skipped
• check_repo: clean
• REUSE: PASS
• build: PASS
• pip check: PASS (isolated environment)
• ROCmDoc conformance: CONFORMANT
• platform artifact validation: PASS (2 bundles)
• git diff --check: PASS