Extracting URLs from CSS @import rule

[yzqzss]

#323
close: #296

This PR adds the ability to extract @import urls at the css extractor level.

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Crawling and archiving these @import urls will be implemented in the next PR.

[Copilot]

Pull Request Overview

This PR adds support for extracting @import URLs from CSS content at the extractor level. Key changes include updating the HTML asset extractor to call the new CSS extraction functions, expanding test coverage for various @import rule scenarios, and refactoring the CSS parser to differentiate between regular URLs and @import URLs.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
internal/pkg/postprocessor/extractor/html.go	Updated to use the new ExtracFromStringCSS function for inline styles and HTML style blocks with appropriate warning log messages.
internal/pkg/postprocessor/extractor/css_test.go	Extended tests to cover multiple @import rule cases and validate error conditions.
internal/pkg/postprocessor/extractor/css.go	Refactored CSS parsing to handle @import rules and introduced helper functions with panic calls for unexpected token types.

Comments suppressed due to low confidence (1)

internal/pkg/postprocessor/extractor/css.go:334

• The function name 'ExtracFromStringCSS' appears to contain a typo. Consider renaming it to 'ExtractFromStringCSS' for clarity and consistency.

func ExtracFromStringCSS(cssBody string, inline bool) (links []string, atImportLinks []string, err error) {

[NGTmeaty]

Looks great! Thanks!