Queuing prompts is slow and gets slower as the queue grows.

To reproduce:

1. Have a workflow. It does not matter what it is, so long as it changes between runs.
2. Set batch size to 100 and click "queue prompt".
3. Repeat.

Expected result:

Adding items to the front or back of a queue should be a linear-time operation, so the time required to queue items should not be affected by the size of the queue.

Actual result:

Time required to queue items grows with the length of the queue. When the queue is empty, queuing 100 items takes about 7 seconds. When the queue contains 500 items, adding another 100 takes 53 seconds. When the queue contains 1000 items, adding another 100 takes 1 minute 47 seconds.

Analysis:

This seems to be partly caused by the use of a heapq rather than a deque (which would more closely match how the queue is actually used and has linear-time operations.) While this explains why the time grows, it can't explain why it is so slow in the first place: there is no way that adding 100 items to a heapq with 1000 items in it should take a minute and a half.