gracefully handle exceptions during MRD and AAOW close

[suni72]

Changes

• Graceful teardown: Added close_mrd and close_aaow utility wrappers to zb_hns_utils.py. These functions gracefully catch and log teardown exceptions as warnings instead of crashing the application.
• Implementation: Replaced direct mrd.close() and aaow.close() calls in ZonalFile and ExtendedGcsFileSystem with the new safe-teardown wrappers.
• Testing: Added unit tests for the closure utilities.

[codecov]

Codecov Report

❌ Patch coverage is 95.23810% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 76.14%. Comparing base (de0ad00) to head (b31452c).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
gcsfs/extended_gcsfs.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #763      +/-   ##
==========================================
+ Coverage   75.88%   76.14%   +0.26%     
==========================================
  Files          19       19              
  Lines        2924     2935      +11     
==========================================
+ Hits         2219     2235      +16     
+ Misses        705      700       -5     

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[ankitaluthra1]

/gcbrun