fix(release): write the native version transform as exact UTF-8 LF bytes

[abrichr]

What

Make set_native_version produce byte-identical output on every platform.

Why

main failed on windows-latest for Python 3.11 and 3.12 after #115:

FAILED tests/test_native_release.py::test_git_version_transform_requires_the_exact_reconstructed_tree
FAILED tests/test_native_release.py::test_git_version_advance_refuses_a_stale_or_equal_target
ValueError: native tag differs from the exact deterministic set-version output:
package.json, package-lock.json, src-tauri/Cargo.toml, src-tauri/Cargo.lock,
src-tauri/tauri.conf.json

validate_git_version_transform reconstructs the five-file transform from the
base ref and compares every byte with the candidate tag's Git blobs, which
store LF. set_native_version wrote those files with Path.write_text, which
opens in text mode and rewrites every \n as \r\n on Windows. Two reads also
omitted encoding=, so they decoded with the locale default. All five files
therefore differed. test.yml runs the Linux lane only for pull requests, so
the exact-head checks on #115 could not see it.

This is a portability defect, not a tag defect. The release workflow runs on
ubuntu-22.04, so no published release was affected — but a byte-exactness
guarantee should not depend on which platform evaluates it.

How

• set_native_version reads and writes all five sources as explicit UTF-8
  bytes, so the transform emits LF everywhere.
• The test fixture writes UTF-8 LF bytes, and each temporary repository sets
  core.autocrlf=false. Git for Windows defaults that to true and would
  otherwise rewrite the very blobs the transform is compared against.
• New test_set_native_version_writes_utf8_lf_bytes_on_every_platform pins the
  invariant so a future text-mode write fails on any runner, not only Windows.

Tests

• Full suite: 1027 passed.
• ruff check engine/ tests/ scripts/: passed.

🤖 Generated with Claude Code