Extracted from bitcoin#33141 (comment).
In Python, list `pop(0)` is linear, so consuming all items is quadratic.
Switched to `collections.deque` with `popleft()` to express FIFO intent and avoid the O(n^2) path.
Behavior is unchanged; for a few hundred items the perf impact is likely negligible.

Ref: https://docs.python.org/3/tutorial/datastructures.html#using-lists-as-queues
> While appends and pops from the end of list are fast, doing inserts or pops
> from the beginning of a list is slow (because all of the other elements have
> to be shifted by one).