testdata synced from datekeys-go 3820066 (verified with sync-testdata
check --against): cbor.json, mutations.json, inspect_differential.json,
the inspect goldens, testdata/README.md and the three new dk1.json
vectors. The alignment of src/lib/dkc and of the vector harness was cut
off by a usage limit halfway through a refactor: tests and typecheck
fail. Kept on this branch so that main stays green; it is finished here
and merged when every check passes.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
