feat: add app-server-test-client crate for internal use (#5391)

For app-server development it's been helpful to be able to trigger some
test flows end-to-end and print the JSON-RPC messages sent between
client and server.

codex-rs/Cargo.lock

@@ -884,6 +884,19 @@ dependencies = [
  "uuid",
 ]
 
+[[package]]
+name = "codex-app-server-test-client"
+version = "0.0.0"
+dependencies = [
+ "anyhow",
+ "clap",
+ "codex-app-server-protocol",
+ "codex-protocol",
+ "serde",
+ "serde_json",
+ "uuid",
+]
+
 [[package]]
 name = "codex-apply-patch"
 version = "0.0.0"