Add nexits average

[Luni-4]

Average NExit over the total number of functions/closures in a space.

Thanks in advance for your review! :)

[codecov-io]

Codecov Report

Merging #333 (39ff9f9) into master (7f33ab1) will increase coverage by 0.10%.
The diff coverage is 63.15%.

@@            Coverage Diff             @@
##           master     #333      +/-   ##
==========================================
+ Coverage   20.11%   20.22%   +0.10%     
==========================================
  Files          48       48              
  Lines        6179     6195      +16     
  Branches      799      803       +4     
==========================================
+ Hits         1243     1253      +10     
- Misses       4421     4423       +2     
- Partials      515      519       +4     

Impacted Files	Coverage Δ
rust-code-analysis-cli/src/web/server.rs	58.91% <ø> (ø)
src/metrics/exit.rs	58.06% <58.82%> (-0.27%)	⬇️
src/spaces.rs	61.84% <100.00%> (+0.50%)	⬆️

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[marco-c]

This needs to be rebased

[Luni-4]

Done