fix(countBy): Support nemeric and symbol keys in `countBy`

[mass2527]

For consistency, the countBy function should support readonly arrays and non-string keys, like groupBy, so I made the change.

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Name	Status	Preview	Comments	Updated (UTC)
es-toolkit	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 26, 2024 1:34pm

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.77%. Comparing base (d02ef35) to head (e8c3d1d).

Additional details and impacted files

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##             main     #433   +/-   ##
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  Coverage   99.77%   99.77%           
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  Files         165      165           
  Lines        1325     1325           
  Branches      357      357           
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  Hits         1322     1322           
  Misses          2        2           
  Partials        1        1