a245bd75a7
Add 67 Go-parity tests from filestore_test.go covering: - SkipMsg/SkipMsgs sequence reservation - RemoveMsg/EraseMsg soft-delete - LoadMsg/LoadLastMsg/LoadNextMsg message retrieval - AllLastSeqs/MultiLastSeqs per-subject last sequences - SubjectForSeq reverse lookup - NumPending with filters and last-per-subject mode - Recovery watermark preservation after purge - FastState NumDeleted/LastTime correctness - PurgeEx with empty subject + keep parameter - Compact _first watermark tracking - Multi-block operations and state verification Implements missing IStreamStore sync methods on FileStore: RemoveMsg, EraseMsg, SkipMsg, SkipMsgs, LoadMsg, LoadLastMsg, LoadNextMsg, AllLastSeqs, MultiLastSeqs, SubjectForSeq, NumPending. Adds MsgBlock.WriteSkip() for tombstone sequence reservation. Adds IDisposable to FileStore for synchronous test disposal.