Improvements to RRC PDU session and DRB handling logic This merge request introduces a major simplification and cleanup of the gNB RRC PDU Sessions and DRBs handling logic. The core goals of this work are to: - Replace fixed-size PDU Session, DRBs and QoS arrays with dynamic containers - Simplify and modularize helper functions for session/DRB management - Prepare for further refactoring of the PDU Session state machine - Improve code safety and maintainability through better bounds checking