fix: preserve how response_error was set prior to #2103

[bolinfest]

I am investigating #4381 and I believe this is the code that is the source of that error today:

codex/codex-rs/core/src/client.rs

Lines 652 to 662 in a43ae86

	let sse = match otel_event_manager
	.log_sse_event(|| timeout(idle_timeout, stream.next()))
	.await
	{
	Ok(Some(Ok(sse))) => sse,
	Ok(Some(Err(e))) => {
	debug!("SSE Error: {e:#}");
	let event = CodexErr::Stream(e.to_string(), None);
	let _ = tx_event.send(Err(event)).await;
	return;
	}

This code was touched recently as part of:

#2103

so this reverts some of the changes to codex-rs/core/src/client.rs introduced in that PR.

While here, promote a number of events that were logging errors from debug!() to error!().