[Saanvi521]

Summary

• Fixes the cost the W8 profile found: the file walk called os.path.relpath once per file (6003 getcwd calls for 3000 files). It now works out each folder once, in one shared walk_working_files() used by status, diff and the name lists.
• status and diff take about 45% less time with many files. Results are identical; every file is still read and hashed, with no cache and no timestamp shortcuts.
• Includes the Week 7 status/diff output, rebased onto current main so M3's merge-resolve code in cmd_add and cmd_status is kept.
• Adds regressions: same-size edit with preserved timestamps is still found, the walk helper's paths, and Myers on a larger text with repeated lines. Before and after timings are in docs/performance.md.

Validation

• scripts/quality-check.sh
• Manual testing, if applicable:

Checklist

• The change is focused and easy to review.
• Tests were added or updated for behavior changes.
• Documentation was updated for user-facing or setup changes.
• No secrets, generated artifacts, or local-only files are included.

Notes for Reviewers

• Numbers should be re-run with the shared benchmark from Week 7 - M4: Network diagnostics + end-to-end performance baseline #47 once it is merged.