push_mut and pop_mut for queues

[orlp]

It would be nice if you could avoid the extra cost of atomic operations + the extra checks done for the lock-free algorithms when you have a mutable reference to the queue (for example during single-threaded initialization of a queue which is then passed off to workers).

[taiki-e]

Seems reasonable to me. I would accept a PR to add this.

[jafar75]

Hi,

@taiki-e I was wondering if it’s okay to submit separate PRs for each queue type (i.e., one for ArrayQueue, another later for SegQueue)? or both of them must be in one PR?
I can send PR for array_queue and after that, I will try to provide one for seg_queue too.