[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/execpolicy/tests/basic.rs

@@ -1,3 +1,4 @@
+#![allow(clippy::expect_used)]
 use std::any::Any;
 use std::fs;
 use std::path::PathBuf;
@@ -35,8 +36,7 @@ fn prompt_all(_: &[String]) -> Decision {
 }
 
 fn absolute_path(path: &str) -> AbsolutePathBuf {
-    AbsolutePathBuf::try_from(path.to_string())
-        .unwrap_or_else(|error| panic!("expected absolute path `{path}`: {error}"))
+    AbsolutePathBuf::try_from(path.to_string()).expect("path should be absolute")
 }
 
 fn host_absolute_path(segments: &[&str]) -> String {