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/app-server-protocol/schema/json/v2/ItemStartedNotification.json

@@ -41,6 +41,7 @@
       "enum": [
         "pendingInit",
         "running",
+        "interrupted",
         "completed",
         "errored",
         "shutdown",