Fix: content scraping and filtering bugs (noscript, preserve, pre/code)

[dajiaohuang]

Summary

Fixes three related content scraping and filtering bugs:

• [Bug]: cleaned_html drops the page body when it is nested inside an unclosed <noscript> #2293: drops page body when nested/unclosed <noscript> tags are present (common with LiteSpeed Cache + Google Tag Manager lazy-load). Added _balance_noscript_tags() pre-processor that inserts missing closing tags before parsing to match browser scripting-enabled behavior.

• [Bug]: preserve_tags/preserve_classes are a no-op for excluded tags (aside, nav, footer, header, form) #2125: preserve_tags/preserve_classes options were silently ignored for excluded tags (aside, nav, footer, header, form). Fixed _remove_unwanted_tags() to skip preserved elements in both BeautifulSoup and LXML implementations. Also added the missing preserve_classes/preserve_tags parameters to PruningContentFilterLXML for API parity.

• PruningContentFilter drops whitespace-only spans in <pre>/<code> — #1181's bug, still present on the fit_markdown path #2110: PruningContentFilter removes whitespace-only spans inside <pre>/<code> blocks (used by syntax highlighters), corrupting code formatting in fit_markdown. Added guard to skip scoring/pruning entirely for pre/code subtrees, matching the fix already applied to remove_empty_elements_fast.

Changes

File	Change
crawl4ai/content_scraping_strategy.py	Add _balance_noscript_tags() to balance malformed noscript tags before lxml parsing
crawl4ai/content_filter_strategy.py	Skip preserved tags in _remove_unwanted_tags(); skip pruning in pre/code blocks
crawl4ai/content_filter_strategy_lxml.py	Accept preserve params; skip preserved tags during strip/metrics/pruning; never prune pre/code children

Validation

• Manual repro for [Bug]: cleaned_html drops the page body when it is nested inside an unclosed <noscript> #2293 confirmed the div/h1/p content is retained in cleaned_html after balancing.
• The pre/code guard prevents low-scoring whitespace spans from being decomposed.
• Preserve tags/classes now prevent excluded boilerplate tags from being removed when explicitly requested.