New CSS parser with go-css-lexer

[yzqzss]

https://github.com/renbaoshuo/go-css-lexer

This is a brand new CSS lexer, which complies with the latest CSS syntax.

The go-css-lexer can handle nested CSS, so in this PR I removed the previous regex fallback parser as well.

cc: @renbaoshuo

---

ref: #345 (comment)

[codecov-commenter]

Codecov Report

❌ Patch coverage is 89.75904% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.50%. Comparing base (66dd982) to head (03874f1).
⚠️ Report is 119 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/pkg/postprocessor/extractor/css.go	92.02%	9 Missing and 2 partials ⚠️
internal/pkg/postprocessor/extractor/css_util.go	78.57%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #415      +/-   ##
==========================================
+ Coverage   55.21%   55.50%   +0.28%     
==========================================
  Files         118      119       +1     
  Lines        7282     7302      +20     
==========================================
+ Hits         4021     4053      +32     
+ Misses       2940     2926      -14     
- Partials      321      323       +2     

Flag	Coverage Δ
e2etests	37.41% <0.00%> (-0.11%)	⬇️
unittests	31.86% <89.75%> (+0.59%)	⬆️

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[NGTmeaty]

Looks great! I'm mostly just curious - but have you ran benchmarks on the old library vs the new one?

[yzqzss]

ExtractFromURLCSS():

old BenchmarkCSS                  494554 ns/op            144378 kB/s   305616 B/op       1702 allocs/op
old_regex BenchmarkCSS            475908 ns/op            150005 kB/s   305613 B/op       1702 allocs/op
csslexer v0.0.2 BenchmarkCSS      931164 ns/op             76681 kB/s   820866 B/op      15560 allocs/op
csslexer v0.0.3 BenchmarkCSS      538515 ns/op            132580 kB/s   447160 B/op         49 allocs/op

I just optimized the go-css-lexer (v0.0.3) and now it's fast enough with minimum memory allocation footprint. renbaoshuo/go-css-lexer#1

[NGTmeaty]

Thanks for the improvements there! That's great!