[ndgrigorian]

As pointed out in #2293, an in-order queue already orders the tasks submitted to it, including tasks submitted by extensions that do not use SequentialOrderManager. What the order manager did not do for such a queue is account for those tasks: SequentialOrderManager[q].wait() returned before them, and submitted_events did not include them, so work on another queue depending on submitted_events could race with them.

This PR:

• adds SyclQueue.get_last_event(), wrapping ext_oneapi_get_last_event() from the DPC++ sycl_ext_oneapi_in_order_queue_events extension
• makes SequentialOrderManager[q] return an _InOrderManager for in-order queues. It keeps only the most recently
  added events. submitted_events is the queue's last event when get_last_event is available, and the most recently added computation events otherwise. wait() waits on the queue.
• caches _InOrderManager in the thread-local map, so clear() at exit and thread exit wait on in-order queues as they do on out-of-order ones.
• types the return value of SequentialOrderManager[q] as OrderManagerProtocol.

• Have you provided a meaningful PR description?
• Have you added a test, reproducer or referred to an issue with a reproducer?
• Have you tested your changes locally for CPU and GPU devices?
• Have you made sure that new changes do not introduce compiler warnings?
• Have you checked performance impact of proposed changes?
• Have you added documentation for your changes, if necessary?
• Have you added your changes to the changelog?
• If this PR is a work in progress, are you opening the PR as a draft?

[github-actions]

View rendered docs @ https://intelpython.github.io/dpctl/pulls/2299/index.html

[coveralls]

coverage: 75.26% (+0.3%) from 74.989% — no-op-order-manager-for-in-order-queues into master

[ndgrigorian]

@antonwolfy @vlad-perevezentsev
this is ready for review, since this impacts order manager, it will impact all of tensor and dpnp. On my tests so far, I have seen no issues, but I will keep trying.

Please experiment with it as well