HBASE-28620 Release inflight buffer when replication source terminates

[Huginn-kio]

HBASE-28620

Summary

When a replication source terminates while a WAL entry batch is in flight, its buffer quota can remain accounted indefinitely.

Root cause

ReplicationSourceShipper.shipEdits polls a WALEntryBatch from the reader queue. The buffer quota is released after successful shipping through postShipEdits; if the worker stops before successful shipping, the batch is no longer in the reader queue and cleanup cannot release its quota.

Fix

• Track whether the polled batch was released by successful shipping.
• Release the batch quota after the shipping loop when it was not successfully shipped.
• Add a regression test for a stopped shipper holding an in-flight batch.

Testing

• Targeted regression test with Maven: 1 test passed, 0 failures, 0 errors, 0 skipped.
• Apache RAT check over the reactor: passed with 0 unapproved and 0 unknown files.
• git diff --check: passed.

Compatibility

• Public API impact: none
• Configuration impact: none
• Persisted format impact: none
• Wire format impact: none