Add app-server startup benchmark crate (#24651)

## Summary
- Add a new `app-server-start-bench` crate to measure app-server startup
performance
- Wire the benchmark into the workspace and Bazel build so it can be run
consistently
- Update lockfiles and repo automation to account for the new package

codex-rs/Cargo.lock

@@ -2058,6 +2058,17 @@ dependencies = [
  "uuid",
 ]
 
+[[package]]
+name = "codex-app-server-start-bench"
+version = "0.0.0"
+dependencies = [
+ "anyhow",
+ "codex-app-server-protocol",
+ "divan",
+ "serde_json",
+ "tempfile",
+]
+
 [[package]]
 name = "codex-app-server-test-client"
 version = "0.0.0"