[Feature] Add URL deep processing architecture

[Feature] Add URL deep processing architecture

This commit implements a two-level URL processing system that addresses
issue #5731 and provides flexible URL analysis with multiple specific symbols.

Core changes:
* Modified src/libserver/url.c to handle oversized user fields (fixes #5731)
* Added lualib/lua_url_filter.lua - Fast library filter during parsing
* Added src/plugins/lua/url_suspect.lua - Deep inspection plugin
* Added conf/modules.d/url_suspect.conf - Plugin configuration
* Added conf/scores.d/url_suspect_group.conf - Symbol scores

Key features:
* No new C flags - uses existing URL flags (has_user, numeric, obscured, etc.)
* Works without maps - built-in logic for common cases
* 15+ specific symbols instead of generic R_SUSPICIOUS_URL
* Backward compatible - keeps R_SUSPICIOUS_URL working
* User extensible - custom filters and checks supported

Optional features:
* Example map files for advanced customization (disabled by default)
* Whitelist, pattern matching, TLD lists

Issue: #5731