[MCP] Add emulator support to firebase storage tools

[tammam-g]

This PR adds emulator support in firebase storage tools. It seems like the only relevant storage tool is get_object_download_url which I confirmed works but uploading a file through the emulator UI interfance and confirming the returned URL downloads the file I uploaded.

Should be reviewed after #8706

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 16.66667% with 5 lines in your changes missing coverage. Please review.

Project coverage is 52.03%. Comparing base (7f80f9f) to head (2a2709f).
Report is 27 commits behind head on master.

Files with missing lines	Patch %	Lines
src/gcp/storage.ts	16.66%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8707      +/-   ##
==========================================
+ Coverage   51.09%   52.03%   +0.93%     
==========================================
  Files         427      407      -20     
  Lines       30930    30263     -667     
  Branches     6350     6266      -84     
==========================================
- Hits        15803    15746      -57     
+ Misses      13715    13100     -615     
- Partials     1412     1417       +5     

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