* chore(python): add support for python 3.11

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* Add python 3.11 to noxfile

* add constraints file

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Co-authored-by: Anthonios Partheniou <partheniou@google.com>

The objects.inv files for two different library deps
are currently inaccessible due to redirects.

In the meantime, allow continuing to build the docs by caching
them locally.

They are second in the list, so if the original URL's
start serving the files themselves, there will be no need
to update conf.py again. The cache is strictly a fallback.

Fixes #862

…p/templates/python_library/.kokoro (#867)

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cc @parthea

They were commented out because testing them in Python 2
was not easy.

In certain circumstances, we were not respecting use_cache
for queries, unlike legacy NDB, which is quite emphatic
about supporting them.
(See https://github.com/GoogleCloudPlatform/datastore-ndb-python/blob/59cb209ed95480025d26531fc91397575438d2fe/ndb/query.py#L186-L187)

In #613 we tried to match legacy NDB behavior by updating the cache
using the results of queries. We still do that, but now we respect
use_cache, which was a valid keyword argument for Query.fetch()
and friends, but was not passed down to the context cache when
needed.

As a result, the cache could mysteriously accumulate lots of memory
usage and perhaps even cause you to hit memory limits, even if it was
seemingly disabled and it didn't look like there were any objects
holding references to your query results.
This is a problem for certain batch-style workloads where you know
you're only interested in processing a certain entity once.

Fixes #752

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