feat: make interrupt state not final for multi-agents (#13850)

Make `interrupted` an agent state and make it not final. As a result, a
`wait` won't return on an interrupted agent and no notification will be
send to the parent agent.

The rationals are:
* If a user interrupt a sub-agent for any reason, you don't want the
parent agent to instantaneously ask the sub-agent to restart
* If a parent agent interrupt a sub-agent, no need to add a noisy
notification in the parent agen

codex-rs/exec/src/exec_events.rs

@@ -228,6 +228,7 @@ pub enum CollabTool {
 pub enum CollabAgentStatus {
     PendingInit,
     Running,
+    Interrupted,
     Completed,
     Errored,
     Shutdown,