Trim whitespace when validating '*** Begin Patch'/'*** End Patch'
markers in codex-apply-patch so padded marker lines parse as intended,
and add regression coverage (unit + fixture scenario); this avoids
apply_patch failures when models include extra spacing. Tested with
cargo test -p codex-apply-patch.
## Summary
Adds a unicode scenario, and fills in files on failing scenarios to
ensure directory state is unchanged, for completeness
## Testing
- [x] only changes tests
## Summary
This PR introduces an End to End test suite for apply-patch, so we can
easily validate behavior against other implementations as well.
## Testing
- [x] These are tests
