fix(filemeta): resolve P2 core-storage audit items B15/B16/B18 (backlog#863)
Fixes the three remaining actionable items from the core-storage reliability
audit (rustfs/backlog#863). All three are metadata-layer correctness defects in
the filemeta crate.
B15 — version sort tie-break consistency
`FileMeta::sort_by_mod_time` and the delete path used a hand-rolled comparator
whose version_type tie-break for equal mod_time was the OPPOSITE of the
canonical `FileMetaVersionHeader::sorts_before` (used by the metacache merge
and latest-version selection). At equal mod_time it sorted a delete marker
before its object, so the per-disk read path could treat an object as deleted
while the quorum-merge path treated it as present. Both sort sites now derive
their ordering from `sorts_before`, matching MinIO (object-first).
B16 — replication reset state persistence
The three sites that flush `reset_statuses_map` into `meta_sys` inserted each
key verbatim. A bare-ARN key (produced by `ObjectInfo::replication_state`) has
no internal prefix, so read-back — which only recognizes prefixed keys —
silently dropped the reset state; a rustfs-only key was invisible to
MinIO-compatible readers. New `persist_reset_statuses` normalizes every entry
to the canonical `replication-reset-<arn>` suffix and writes both the
`x-rustfs-internal-*` and `x-minio-internal-*` prefixes.
B18 — Legacy (V1Obj) body round trip
`FileMetaVersion::encode_to` never emitted the `V1Obj` field, so re-encoding a
Legacy version silently dropped its entire body. Adds symmetric `encode_to`
for `MetaObjectV1`/Stat/Erasure/ChecksumInfo/Part and a `write_msgp_time`
helper (ext8/type-5/12-byte, matching the decoder). `Mode` uses the strict
`write_u32` marker the decoder requires, and `Stat.ModTime` is written only
when present so a `None` never round-trips to `Some(UNIX_EPOCH)`.
Adds regression tests for each fix (138 filemeta tests pass). Verified with an
adversarial multi-expert review that could not break any of the three.
Refs rustfs/backlog#863 (B15, B16, B18).
