[codex] Use expect in integration tests (#28441)

The workspace denies `clippy::expect_used` in production. Although
`clippy.toml` allows `expect` in tests, Bazel Clippy compiles
integration-test helper code in a way that does not receive that
exemption, which encouraged verbose `unwrap_or_else(... panic!(...))`
and equivalent `match`/`let else` forms.

This allows `clippy::expect_used` once at each integration-test crate
root (including aggregated suites and test-support libraries), then
replaces manual panic-based Result and Option unwraps with
`expect`/`expect_err`. Standalone `tests/*.rs` files remain their own
crate roots. Intentional assertion and unexpected-variant panics remain
unchanged, and the production `expect_used = "deny"` lint remains in
place.

The cleanup is mechanical and net-negative in line count.

codex-rs/login/tests/all.rs

@@ -1,3 +1,5 @@
+#![allow(clippy::expect_used)]
+
 // Single integration test binary that aggregates all test modules.
 // The submodules live in `tests/suite/`.
 mod suite;

codex-rs/login/tests/suite/auth_refresh.rs

@@ -1295,14 +1295,8 @@ fn jwt_with_payload(payload: serde_json::Value) -> String {
         base64::engine::general_purpose::URL_SAFE_NO_PAD.encode(data)
     }
 
-    let header_bytes = match serde_json::to_vec(&header) {
-        Ok(bytes) => bytes,
-        Err(err) => panic!("serialize header: {err}"),
-    };
-    let payload_bytes = match serde_json::to_vec(&payload) {
-        Ok(bytes) => bytes,
-        Err(err) => panic!("serialize payload: {err}"),
-    };
+    let header_bytes = serde_json::to_vec(&header).expect("header should serialize");
+    let payload_bytes = serde_json::to_vec(&payload).expect("payload should serialize");
     let header_b64 = b64(&header_bytes);
     let payload_b64 = b64(&payload_bytes);
     let signature_b64 = b64(b"sig");

codex-rs/login/tests/suite/login_server_e2e.rs

@@ -75,7 +75,7 @@ fn start_mock_issuer(chatgpt_account_id: &str) -> (SocketAddr, thread::JoinHandl
                 let mut resp = tiny_http::Response::from_data(data);
                 resp.add_header(
                     tiny_http::Header::from_bytes(&b"Content-Type"[..], &b"application/json"[..])
-                        .unwrap_or_else(|_| panic!("header bytes")),
+                        .expect("header bytes should be valid"),
                 );
                 let _ = req.respond(resp);
             } else {