Redis-throttled-queue

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* Switched from eval scripts to redis functions. Minimum Redis server version becomes 7.0.
* Replaced unpack calls with direct indexing in the Lua functions.
* These changes improve the push operation by at least 6%.

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* Simplified ``pop()`` code to avoid the expensive scan operations.
The ``'...:names`` key is now a sorted set and will be used as a template for the usage keys (``'...:usage:<window>'``).

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* Added support in a ``AsyncThrottledQueue`` class that only differs a bit from the regular ``ThrottledQueue``:

* ``__len__`` is removed, instead a awaitable ``size()`` method is available.
* ``__init__`` doesn't validate version anymore, instead you can await on ``validate_version()``.
* ``push()``, ``pull()`` and ``cleanup()`` are awaitable.
* Added a ``validate_version`` argument to ``ThrottledQueue`` (default: ``True``).

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* Fixed missing usage key expiration when some queues are empty.

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* Fixed buggy counts when duplicate values are pushed.
For now the highest priority will be used when two identical
values would be pushed.

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* Refactored some duplicated code in the `pop` script.