This is a basic implementation of a first-in-first-out queue with unbounded
size. It's useful for cases where a channel with fixed size might deadlock.

The caller is responsible for locking.

Step simplifies using WithStep because it creates a local scope where the same
tCtx variable is the one with the step name.

This enables using the assume cache for cluster events.

This enables connecting the event handler for ResourceClaim to the assume
cache, which addresses a theoretic race condition.

It may also be useful for implementing the autoscaler support, because now
the autoscaler can modify the content of the cache.