Optimize charWhere for Sets

[johnynek]

Since Set[Char] extends Char => Boolean but we can also enumerate it directly, we can directly call charIn rather than exhaustively checking the function.

[codecov-commenter]

Codecov Report

Merging #288 (ea01e47) into main (eee5032) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #288   +/-   ##
=======================================
  Coverage   96.36%   96.37%           
=======================================
  Files           8        8           
  Lines         991      992    +1     
  Branches       95       91    -4     
=======================================
+ Hits          955      956    +1     
  Misses         36       36           

Impacted Files	Coverage Δ
core/shared/src/main/scala/cats/parse/Parser.scala	96.28% <100.00%> (+<0.01%)	⬆️

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[regadas]

👍 really nice one!