Optimize Not error condition

[johnynek]

We use Eval to defer doing any work except allocation on errors since oneOf can recover failures. So we don't actually want to run the error condition until the end.

Not was allocating a copy of a string before the Eval so that allocation had to happen on every failure, which could be a lot for some cases. By moving the allocation inside the Eval we will (almost certainly) save.

[codecov-commenter]

Codecov Report

Merging #363 (aa15a7e) into main (828ff4b) will increase coverage by 0.09%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #363      +/-   ##
==========================================
+ Coverage   96.63%   96.72%   +0.09%     
==========================================
  Files           9        9              
  Lines        1128     1130       +2     
  Branches       99       99              
==========================================
+ Hits         1090     1093       +3     
+ Misses         38       37       -1     

Impacted Files	Coverage Δ
core/shared/src/main/scala/cats/parse/Parser.scala	96.70% <100.00%> (+0.11%)	⬆️

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