[kv] Fix flaky KvTabletSnapshotTargetTest.testAddToSnapshotToStoreFail

[Kaixuan-Duan]

Purpose

Linked issue: close #2624

Brief change log

• Reorder KvTabletSnapshotTarget#updateStateOnCommitSuccess so the outward-visible updates happen first:
  1.assign logOffsetOfLatestSnapshot
  2.assign snapshotSize
  3.invoke updateMinRetainOffset.accept(flushedLogOffset)
  4.then (in finally) invoke rocksIncrementalSnapshot.notifySnapshotComplete(snapshotId)
• The RocksDB bookkeeping call is wrapped in a finally block so the internal uploadedSstFiles cleanup is guaranteed even if an outward update throws in the future.

Tests

./mvnw -pl fluss-server test -Dtest='KvTabletSnapshotTargetTest#testAddToSnapshotToStoreFail'

API and Format

No API or storage format change.

Documentation

No user-facing documentation change.