Agent & entanglement rust implementation

[fayeed]

No description provided.

[lucksus]

I didn't want to block this PR only because of the env var thing, but if we have more changes then that should be improved as well.

But the main change request I have is, not having a good portion of added lines be the same

let agent_instance = AgentService::instance();
let agent_service = agent_instance.lock().expect("agent lock");
let agent_ref: &AgentService = agent_service.as_ref().expect("agent instance");

over and over again. Adding something like Ad4mDb::with_global_instance() to AgentService (or all our singletons) will reduce noice and deadlock risk.