Replacing the regex-based CSS extractor with a standard CSS parser

[yzqzss]

#323

The most complete golang css parsing library I've found is https://github.com/tdewolff/parse/, but it returns the entire token as is, for example, if you let it to parse uRl( "http://a\"b\e9 c" ), it will just return a data structure like:
{TokenType: URLToken, Data: []byte(`uRl( "http://a\"b\e9 c" )`) }
and won't parse and return the actual value (http://a"béc) for you.

Therefore, I wrote a small parser function parseStringOrURLTokenData() to extract value from token data.

[Copilot]

Pull Request Overview

This PR refactors the URL extraction from in-html CSS by replacing regex-based extraction with a dedicated CSS parser, and it adds comprehensive tests for various CSS URL patterns.

• Replaces regex extraction in html.go with a call to a new CSS() function.
• Adds a new css.go file implementing the CSS parsing logic.
• Introduces css_test.go to thoroughly validate CSS URL extraction behavior.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

File	Description
internal/pkg/postprocessor/extractor/html.go	Removed regex extraction and replaced with CSS() function call
internal/pkg/postprocessor/extractor/css_test.go	Added tests covering various CSS URL extraction scenarios
internal/pkg/postprocessor/extractor/css.go	Introduces the new CSS parser functions and helper methods
go.mod	Updated dependency to github.com/tdewolff/parse/v2 v2.8.1

Comments suppressed due to low confidence (1)

internal/pkg/postprocessor/extractor/css.go:226

• [nitpick] The empty else block can be removed as it does not add any functionality and only clutters the code.

else { }

[NGTmeaty]

Looks great! Thank you for your contribution! This should massive improve our extraction!

[NGTmeaty]

Looks great. Thank you for the improvements here and great job! I can't wait to see the rest of the CSS PRs come through! They will be extremely impactful for Zeno!