fix(patch): handle diff.noprefix and normalize non-standard diff paths

libgit2 respects the user's `diff.noprefix` git config when generating
patches via `git_email_create_from_commit`, producing diffs without the
standard `a/`/`b/` path prefixes. `git2::Diff::from_buffer` always
expects the standard prefix format and fails with "header filename does
not contain 1 path components" when it is absent.

Two fixes:
- In `make_patch_from_commit`: explicitly set `old_prefix("a/")` and
  `new_prefix("b/")` on the diff options so ngit always generates
  interoperable patches regardless of the submitter's git config.
- In `create_commit_from_patch`: normalize no-prefix diffs before
  passing to `git2::Diff::from_buffer`, as a defensive measure for
  patches already published by affected ngit versions or other tools.

Adds unit tests for the normalization function covering: no-op on
already-prefixed diffs, single and multi-file patches, new/deleted
files (/dev/null preservation), and end-to-end libgit2 parse
verification.

0 files changed, 0 insertions, 0 deletions