Reworked the proxy creation used by scoped_session() to be
based on fully copied code with augmented docstrings and
moved it into langhelpers.  asyncio session, engine,
connection can now take
advantage of it so that all non-async methods are availble.

Overall implementation of most important accessors / methods
on AsyncConnection, etc. , including awaitable versions
of invalidate, execution_options, etc.

In order to support an event dispatcher on the async
classes while still allowing them to hold __slots__,
make some adjustments to the event system to allow
that to be present, at least rudimentally.

Fixes: #5628
Change-Id: I5eb6929fc1e4fdac99e4b767dcfd49672d56e2b2

Fixes: #5223
Change-Id: I0952e54ed9af2952ea340be1945311376ffc1ad2

pytest has removed support for pytest.Class().collect()
and we need to use from_parent.

Change-Id: Ia5fed9b22e76c99f71489283acee207f996f52a4

Added the :class:`_schema.Identity` construct that can be used to
configure identity columns rendered with GENERATED { ALWAYS |
BY DEFAULT } AS IDENTITY. Currently the supported backends are
PostgreSQL >= 10, Oracle >= 12 and MSSQL (with different syntax
and a subset of functionalities).

Fixes: #5362
Fixes: #5324
Fixes: #5360

Change-Id: Iecea6f3ceb36821e8b96f0b61049b580507a1875

With version 2.0.0 they removed the old terminology, which
I had no idea had been changed in any case for several years.

pushing this out for all branches

Change-Id: I51e4f577aeb9ef8205348b50489549f77072a613

Using the approach introduced at
https://gist.github.com/zzzeek/6287e28054d3baddc07fa21a7227904e

We can now create asyncio endpoints that are then handled
in "implicit IO" form within the majority of the Core internals.
Then coroutines are re-exposed at the point at which we call
into asyncpg methods.

Patch includes:

* asyncpg dialect

* asyncio package

* engine, result, ORM session classes

* new test fixtures, tests

* some work with pep-484 and a short plugin for the
  pyannotate package, which seems to have so-so results

Change-Id: Idbcc0eff72c4cad572914acdd6f40ddb1aef1a7d
Fixes: #3414

Note the PR has a few remaining doc linking issues
listed in the comment that must be addressed separately.

Signed-off-by: aplatkouski <5857672+aplatkouski@users.noreply.github.com>
Closes: #5371
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/5371
Pull-request-sha: 7e7d233cf3a0c66980c27db0fcdb3c7d93bc2510

Change-Id: I9c36e8d8804483950db4b42c38ee456e384c59e3

Change-Id: I431e1ef41e26d490343204a75a5c097768749768

py.test 5.4.0 emits deprecation warnings for pytest.Class.
make sure we don't raise for these, and log the code that will
be used for 5.4.0 when we bump requirements.

Fixes: #5201
Change-Id: I83e0402c4a6b2365a63b58d052c6989df3a37328

The technique arrived at for doing exclusions inside of combinations
relies upon comparing all the arguments in a particular combination
to some set of combinations that were gathered as having
"exclusions".   This logic is actually broken for the
case where the @testing.combinations has an "id", but if we fix
that, we still have the issue of all the arguments being
compared, which is complicated and also doesn't work for the
case of a py2/py3 incompatibility like a timezone that has
fractional minutes or seconds in it.   It's also not clear
if a @testing.combinations that uses lambdas will work either
(maybe it does though because lambdax == lambdax compares...).

anyway, this patch reworks it so that we hit this on the decorator
side instead, where we add our own decorator and go through
the extra effort to create a decorator that accepts an extra
argument of "exclusions" which we can then check in a way that
is local to the whole pytest @combinations thing in the first place.
The only difficulty is that pytest is very sneaky about looking
at the test function so we need to make sure __wrapped__ isn't
set when doing this.

Change-Id: Ic57aae15b378e0f4ed009e4e82ae7ba73fb6dfc5