Document intentional non-caching and fallback behavior for UNKNOWN bucket layouts

[Yonghui-Lee]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.13%. Comparing base (991faba) to head (09f401a).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
gcsfs/extended_gcsfs.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #844      +/-   ##
==========================================
+ Coverage   88.52%   89.13%   +0.61%     
==========================================
  Files          15       15              
  Lines        2989     3130     +141     
==========================================
+ Hits         2646     2790     +144     
+ Misses        343      340       -3     

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[ankitaluthra1]

Not caching UNKNOWN type is intentional, since the storage_lookup api should work on every bucket. In case bucket type is UNKNOWN it surely is a transient error and should not be cached. I think we should revert caching UNKNOWN in this PR and can update the documentation instead so its clearer that its an intentional change