🧪 Add test coverage for resolve_pull_request_context

[joy7758]

🎯 What: Added comprehensive test coverage for the previously untested resolve_pull_request_context function.
📊 Coverage: Tests now cover explicit argument handling, environment variable fallback, TITMAS variable precedence, invalid inputs, and reading pull request information from the GITHUB_EVENT_PATH payload.
✨ Result: Enhanced the overall reliability and coverage of the PR gate logic by ensuring the pull request context resolution logic correctly handles GitHub Actions and manual environments.

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PR created automatically by Jules for task 18002365165637998200 started by @joy7758

[google-labs-jules]

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