[Open311] Handle base64-encoded data URIs when fetching updates/reports

[davea]

Add support for decoding base64-encoded data URIs when processing media URLs. The method now checks for the ;base64 marker and decodes the data appropriately.

For FD-6433

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.65%. Comparing base (08bfe41) to head (b5657b5).

Files with missing lines	Patch %	Lines
perllib/Open311.pm	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5785      +/-   ##
==========================================
+ Coverage   82.64%   82.65%   +0.01%     
==========================================
  Files         457      457              
  Lines       35716    35721       +5     
  Branches     5822     5824       +2     
==========================================
+ Hits        29516    29524       +8     
  Misses       4501     4501              
+ Partials     1699     1696       -3     

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