Coroutines are marked as performance critical context

Almost all coroutines are marked as performance critical context. Often this does not seem justified. E.g.:
```
// Called from Start()
private IEnumerator PlaySoundSequence()
{
yield return new WaitForSeconds(delay);
PlaySound(sound);
}
```
Seemingly randomly some are not marked. What's the pattern here? Should this be the case?

Use the PlaySoundSequence coroutine called from Start() as the reproduction case, and compare it with coroutines that are not marked as performance-critical. Determine the rule behind the differing annotations and whether the example is incorrectly classified. Done means the behavior is explained and any required correction is covered by a reproducible check.

Written by the indexing model from the issue text.