Write stats to cache_stats_file after compile

[zmc]

Fixes: #33

This would be my first contribution to this project, and I am relatively inexperienced with Rust, so I'd love feedback on this.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 58.20896% with 28 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.70%. Comparing base (a888c16) to head (9d35321).

Files with missing lines	Patch %	Lines
src/server.rs	52.63%	27 Missing ⚠️
tests/oauth.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2452      +/-   ##
==========================================
+ Coverage   71.62%   71.70%   +0.08%     
==========================================
  Files          65       65              
  Lines       36459    36476      +17     
==========================================
+ Hits        26112    26155      +43     
+ Misses      10347    10321      -26     

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[sylvestre]

did you evaluate the perf impact of this? thanks

[ahartmetz]

What's the use case for this? It seems pretty exotic. I don't really mind since it's opt-in, anyway...