Add ruff check & ternary RLLM review mode

[ChengZhang-98]

Summary

• Add ruff check to CI and justfile lint target alongside existing ruff format --check
• Extend reduced_grammar_for_rllm_review from bool | None to Literal["none", "bool", "text"] | bool | None for finer-grained control over RLLM review paraphrasing
• Fix lint warnings (unused imports/variables) across test files

Test plan

• CI passes ruff check and ruff format --check
• Existing tests pass with updated imports
• Verify reduced_grammar_for_rllm_review accepts "none", "bool", "text", true, false, and null

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