[Fix] Enable FALLBACK mode for RE multipatterns (stop words)

[Fix] Enable FALLBACK mode for RE multipatterns (stop words)

- Create pats array for all multipatterns, not just TLD
- Use rspamd_multipattern_build_acism() for proper RE fallback
- Add regex fallback path in lookup while HS is compiling
- Clean up mp->res in destructor for hyperscan path

This fixes stop words multipatterns which use RSPAMD_MULTIPATTERN_RE
to properly use FALLBACK mode instead of falling through to SYNC mode
and creating .hs files during config loading.