Support arbitrary ldapfilters via AST parsing and internal backend querying

[runleveldev]

Currently, the LDAPServer only supports a limited set of hardcoded LDAP filters using regex parsing. This restricts the ability to perform complex queries using the LDAP protocol. To improve flexibility and standards compliance:

• The directory backend should be enhanced to parse LDAP filters into an Abstract Syntax Tree (AST).
• The backend should maintain an internal representation (IR) that can be queried using the AST, enabling support for arbitrary LDAP filters beyond the current hardcoded list.
• The implementation should replace the regex-based approach and provide full compatibility with standard LDAP search filters.

This change will allow clients to use a broader range of filter types and expressions when querying the directory.