Some performance improvements

[FollowTheProcess]

Summary

Implement some perf improvements from reading https://github.com/golang/example/blob/master/slog-handler-guide/README.md#general-considerations.

I know this isn't a slog.Handler but the same tricks apply!

[codecov]

Codecov Report

❌ Patch coverage is 93.82716% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.66%. Comparing base (511c952) to head (c8a916b).

Files with missing lines	Patch %	Lines
log.go	95.58%	2 Missing and 1 partial ⚠️
level.go	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #39      +/-   ##
==========================================
- Coverage   96.36%   86.66%   -9.70%     
==========================================
  Files           3        3              
  Lines         110      150      +40     
==========================================
+ Hits          106      130      +24     
- Misses          3       19      +16     
  Partials        1        1              

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