[Fix] re_cache: Always use charset-converted content for SARAWBODY matching

[Fix] re_cache: Always use charset-converted content for SARAWBODY matching

Use utf_raw_content (charset-converted UTF-8 with HTML tags preserved)
for all SARAWBODY patterns, regardless of /u flag presence. The previous
approach used utf_content (which strips HTML tags on HTML parts) and only
for classes containing /u patterns, leaving non-/u patterns matching
against raw bytes in the original charset.

This prevents trivial bypass of SA rawbody rules via exotic encodings
like UTF-16 and ensures consistent matching across PCRE and Hyperscan.
Falls back to transfer-decoded parsed content only when charset
conversion failed.