feat(runtime): expose resident driver boundaries

Expose exact Actor instance identity and manifest mailbox capacity so Host supervisors can distinguish idempotent starts from fault recovery and preserve revision-specific limits.

Expose resident stream chunk and endpoint-policy validation to drivers, and mark terminal streams closing before dispatching their final callback.

Cover Actor identity reuse and replacement in the Runtime integration suite.

crates/wasmeld-runtime/tests/runtime_components.rs

@@ -96,12 +96,16 @@ fn faulted_actor_can_be_started_again() {
     let runtime = Runtime::new(RuntimeConfig::default()).expect("runtime should start");
     let (key, actor) = start_component(&runtime, "fault", "fault_component.wasm");
 
+    let already_running = runtime.start(&key, Vec::new()).unwrap();
+    assert!(actor.is_same_instance(&already_running));
+
     assert!(matches!(
         actor.invoke(b"fault".to_vec()),
         Err(RuntimeError::ActorFault { .. })
     ));
 
     let restarted = runtime.start(&key, Vec::new()).unwrap();
+    assert!(!actor.is_same_instance(&restarted));
     assert_eq!(restarted.invoke(b"ready".to_vec()).unwrap(), b"ready");
 
     runtime.stop(&key).unwrap();