feat(install): seed deno.lock from yarn.lock
Extend the lockfile seeding hook to also accept yarn classic (v1)
lockfiles. When `deno install` runs with no deno.lock,
no package-lock.json, and no pnpm-lock.yaml, but a yarn.lock is
present, its blocks are translated and used to seed the new deno.lock.
Yarn classic's custom (non-YAML) lockfile format is hand-parsed; the
required structure is well-bounded (block header with comma-separated
patterns, two-space-indented properties, four-space-indented
dependency lines).
Yarn berry (v2+) lockfiles are detected via the `__metadata` key and
rejected with a clear error: berry's `checksum` values are typically
xxhash rather than SRI-compatible sha-512 digests, so translating
them without losing integrity is not possible without re-fetching.
