upload_song: add error when file exceeds limit of 300MB

[sigma67]

(closes #647)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.15%. Comparing base (7d062c2) to head (9378e12).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #653      +/-   ##
==========================================
+ Coverage   95.14%   95.15%   +0.01%     
==========================================
  Files          38       38              
  Lines        2285     2293       +8     
==========================================
+ Hits         2174     2182       +8     
  Misses        111      111              

Flag	Coverage Δ
unittests	95.15% <100.00%> (+0.01%)	⬆️

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