Use cow-utils instead

[heygsc]

close: #4123

[codecov]

Codecov Report

Attention: Patch coverage is 11.11111% with 8 lines in your changes missing coverage. Please review.

Project coverage is 53.76%. Comparing base (6ddc2b4) to head (b73c9f3).
Report is 349 commits behind head on main.

Files with missing lines	Patch %	Lines
core/macros/src/lib.rs	0.00%	5 Missing ⚠️
core/engine/src/builtins/string/mod.rs	0.00%	2 Missing ⚠️
.../engine/src/builtins/temporal/zoneddatetime/mod.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4133      +/-   ##
==========================================
+ Coverage   47.24%   53.76%   +6.51%     
==========================================
  Files         476      485       +9     
  Lines       46892    48456    +1564     
==========================================
+ Hits        22154    26050    +3896     
+ Misses      24738    22406    -2332     

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[CrazyboyQCD]

Please wait for #4134 to get merged, so that to_string could be removed on those conversions to avoid one extra allocation.