Apply the negotiated DSCP value to the UDP socket after a successful session open and clear it before closing to support network-level quality of service. This change adds platform-specific socket option handling for IPv4 TOS and IPv6 Traffic Class.
Introduce a BackendPeer abstraction to transparently switch between fake and real IRTT backends. This simplifies test logic by removing manual skip checks and providing a consistent interface for server lifecycle management.
Introduce a mechanism to run tests against a live irtt binary to verify real-world protocol interoperability, including HMAC authentication and various timestamp modes.