Don't retry "insufficient_quota" errors (#6340)

This PR makes an "insufficient quota" error fatal so we don't attempt to
retry it multiple times in the agent loop.

We have multiple bug reports from users about intermittent retry
behaviors, and this could explain some of them. With this change, we'll
eliminate the retries and surface a clear error message.

The PR is a nearly identical copy of [this
PR](https://github.com/openai/codex/pull/4837) contributed by
@abimaelmartell. The original PR has gone stale. Rather than wait for
the contributor to resolve merge conflicts, I wanted to get this change
in.

codex-rs/core/tests/suite/mod.rs

@@ -26,6 +26,7 @@ mod model_overrides;
 mod model_tools;
 mod otel;
 mod prompt_caching;
+mod quota_exceeded;
 mod read_file;
 mod resume;
 mod review;