[Fix] Use void* for lua_state in public API

[Fix] Use void* for lua_state in public API

- Change lua_State* to void* in url.h public functions
- Fixes C compilation: struct lua_State and lua_State are distinct types in C
- Cast void* to lua_State* inside implementation (url.c)
- Updated: rspamd_url_parse(), rspamd_url_find_multiple()
- Updated: rspamd_web_parse() internal function
- Updated: url_callback_data structure
- Follows C convention: opaque pointers in public headers