test(send queue): cached thumbnails of unknown dimensions are removed after upload

[bnjbvr]

When we don't know the dimensions of a thumbnail, we still need some dimensions to cache it locally in the cache store, because it's required to send the thumbnail with the send queue. As a result, we default to using 0 for the unknown dimensions.

However, as soon as the thumbnail and file have been uploaded, there's no need to keep the 0-sized thumbnail in the cache; it's more likely the callers will try to retrieve it with actual, realistic sizes later. As a result, remove those locally-cached thumbnails from the cache store after a successful upload, if one of their dimensions was unknown.

Part of #4201

[codecov]

Codecov Report

Attention: Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.

Project coverage is 84.99%. Comparing base (c02d8ce) to head (4bd8818).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/matrix-sdk/src/send_queue/upload.rs	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4260      +/-   ##
==========================================
+ Coverage   84.96%   84.99%   +0.02%     
==========================================
  Files         274      274              
  Lines       29851    29857       +6     
==========================================
+ Hits        25362    25376      +14     
+ Misses       4489     4481       -8     

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[stefanceriu]

Makes sense to me! 👌