remove various toString calls

[neheb]

std::format is more efficient.

[codecov]

Codecov Report

Attention: Patch coverage is 48.71795% with 20 lines in your changes missing coverage. Please review.

Project coverage is 63.89%. Comparing base (2e6fb08) to head (065ae39).
Report is 32 commits behind head on main.

Files with missing lines	Patch %	Lines
src/quicktimevideo.cpp	45.94%	20 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3244      +/-   ##
==========================================
- Coverage   63.91%   63.89%   -0.03%     
==========================================
  Files         104      104              
  Lines       21752    21726      -26     
  Branches    10636    10639       +3     
==========================================
- Hits        13903    13881      -22     
+ Misses       5641     5637       -4     
  Partials     2208     2208              

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[kmilos]

I know it's more verbose since the cast would come out, but I kind of prefer bool operator==(const char* key) const; as it conveys the meaning better? OTOH, this is an internal implementation detail...