SDSTOR-20656: clear wbc chunk selector

[nnastonen]

0. Create homestore with chunk selector
1. Create btree1 and populate it
2. Nodes get into wbc cache
3. Destroy btree1 (wbc purge is not done, also volume's chunk bitmap is not cleared)
4. Create btree2 and populate it
5. Nodes get into wbc cache and we get cache corruption, duplicate inserts

This change makes chunk release asynchronous and defers returning the chunk to the free pool until cleanup is complete.

New flow:

• detach the volume's chunk list from m_volume_chunks
• run asynchronous cleanup for all the chunks
• in cleanup, evict all allocated blkids for the chunks from WBC
• [reset the chunks' block allocator state (bitmap)]
• reinsert the chunks into m_per_dev_chunks

This PR also addresses this ticket SDSTOR-20651

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

❌ Patch coverage is 41.35338% with 78 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (dev/v6.x@d2e0087). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/lib/volume/volume_chunk_selector.cpp	40.00%	27 Missing and 51 partials ⚠️
❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@             Coverage Diff             @@
##             dev/v6.x     #179   +/-   ##
===========================================
  Coverage            ?   47.57%           
===========================================
  Files               ?       19           
  Lines               ?     1299           
  Branches            ?      573           
===========================================
  Hits                ?      618           
  Misses              ?      295           
  Partials            ?      386           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.