fix: memory leak in CompactionUploader during shutdown

[vishalmaurya850]

Fix memory leak in CompactionUploader during shutdown

More detailed description of your change, if necessary.

During shutdown, CompactionUploader leaked ByteBuf objects allocated by ProxyWriter.ObjectWriter because in-flight writeStreamObject operations were not aware that the uploader was shutting down.

Root cause: shutdown() never set isAborted = true. This allowed in-flight lambdas in writeStreamObject and prepareObjectAndWrite to pass the abort check, allocate a DataBlockWriter (which allocates a CompositeByteBuf internally), and then chain writes on a pool that was terminating. If pending StreamDataBlock.getDataCf() futures never completed (because upstream readers were also shutting down), the future chain hung indefinitely and the whenComplete cleanup handler was never invoked — leaking the writer's internal buffer.

Changes:

• Set isAborted = true in shutdown() so in-flight operations bail out early.
• Release streamSetObjectWriter after pools terminate in shutdown().
• Add a double-check of isAborted in writeStreamObject() immediately after DataBlockWriter allocation to close the race window between the first check and writer creation.
• Add an isAborted guard in prepareObjectAndWrite() before writing to the stream-set object writer.

Issue

Fixes #2364

Summary of testing strategy

• Existing CompactionUploaderTest (unit tests for writeStreamObject, chainWriteStreamSetObject) continues to pass, confirming no regression in the happy path.
• The fix is a defensive shutdown guard — the race condition is inherently timing-dependent and difficult to reproduce deterministically in a unit test. Verification relies on the absence of ResourceLeakDetector LEAK warnings in integration/E2E runs under repeated compaction-shutdown cycles.
• Netty's ResourceLeakDetector (set to PARANOID in test environments) will surface any remaining leaks if the fix is incomplete.

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)