Eryk Sun: Well, I think step 1 should be to update the documentation for Python 3.7 through 3.10 on `subprocess.run()` and `subprocess.TimeoutExpired` to clearly state that `TimeoutExpired.stdout` and `TimeoutExpired.stderr` will be in bytes format even if text mode is set.

If we went with the model of having `stdout_bytes` and attempting to decode into `stdout`, we'd want an option to ignore a trailing decoding error.