Drop the legacy unified-diff patch parameter and all related parsing/
generation logic (_parse_patch, _generate_patch, _apply_hunks, etc.).
The tool now accepts only the structured `edits` array, eliminating the
intermediate diff-string round-trip.
Also update file_edit_events tracking and tests to work exclusively
with edits.
Benchmark (zhipu glm-5.1, edits mode): 15/15 cases passed.