fix: introduce EventMsg::TurnAborted (#2365)

Introduces `EventMsg::TurnAborted` that should be sent in response to
`Op::Interrupt`.

In the MCP server, updates the handling of a
`ClientRequest::InterruptConversation` request such that it sends the
`Op::Interrupt` but does not respond to the request until it sees an
`EventMsg::TurnAborted`.

codex-rs/mcp-server/src/codex_tool_runner.rs

@@ -272,6 +272,7 @@ async fn run_codex_tool_session_inner(
                     | EventMsg::TurnDiff(_)
                     | EventMsg::GetHistoryEntryResponse(_)
                     | EventMsg::PlanUpdate(_)
+                    | EventMsg::TurnAborted(_)
                     | EventMsg::ShutdownComplete => {
                         // For now, we do not do anything extra for these
                         // events. Note that