Use uv to speedup tests on CI

[hugovk]

Reduces human waiting time from 2m 57s (total machine time 13m 18s) to 1m 38s (9m 17s).

https://github.com/hugovk/em-keyboard/actions/runs/10647681519/usage

->

https://github.com/hugovk/em-keyboard/actions/runs/10647730921/usage

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.45%. Comparing base (8ccef3c) to head (8108c23).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #144      +/-   ##
==========================================
+ Coverage   93.96%   98.45%   +4.48%     
==========================================
  Files           2        2              
  Lines         199      194       -5     
==========================================
+ Hits          187      191       +4     
+ Misses         12        3       -9     

Flag	Coverage Δ
macos-latest	93.81% <ø> (+1.85%)	⬆️
ubuntu-latest	?
windows-latest	94.32% <ø> (?)

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