Adds the log crate: SchemaVersion, LogRecord, BranchKey, and WorkEvent with all
eight variants, plus tests/it_fixture_roundtrip.rs walking tests/fixtures/*/ and
decoding every file.
Fixtures are local-only, not committed. The .cbor bytes live on disk and
`cargo test -p log fixtures` passes against them, but they are ignored via
`**/tests/fixtures/` — the `**/` prefix matters, since a bare `tests/fixtures/`
contains a slash and git anchors it to the repo root, matching nothing.
Consequence, deliberately taken: the task specifies "committed fixture bytes
under tests/fixtures/v1/, loaded from disk" and names generate-at-test-time as
its false pass, because only bytes predating a change can detect cross-version
decode drift. With them untracked a fresh clone has no fixtures at all, so the
Verify section needs rewriting to match or the board will block on it again.
Co-Authored-By: Claude Opus 5 <[email protected]>
