Opening this in favor of #9383 -- that PR also included all of the
breaking changes to unify function signatures and it was too much at
once. This PR adds only the signature checking mechanism, plus the
requisite xfails to lay out which inconsistencies are currently in Ibis.

## Motivation

We want to ensure that, for a given backend, that the argument names,
plus usage of positional, positional-only, keyword, and keyword-only
arguments match, so that there is API consistency when moving between
backends.

I've grabbed a few small parts of some of the utilities in Scott
Sanderson's
`python-interface` project
(https://github.com/ssanderson/python-interface).

While the upstream is no longer maintained, the goal of that project
aligns quite well with some of the issues we face with maintaining
consistent interfaces across backends.

Note that while the upstream project focused on _runtime_ enforcement of
these signatures matching, here it is only run in the test suite.

## Rough procedure

Any method that doesn't match can be skipped entirely (this is useful
for things like `do_connect`, which cannot reasonably be assumed to
match) or individually (by specifying a `pytest.param` and marking the
failing backends).

Then we scrape across the common parent classes and add any methods that
are NOT currently specified in the pre-existing xfailed ones. It's a bit
of a nuisance, but it's done, and ideally the manual listing of the
inconsistent methods goes away as we unify things.


I've opted for not checking that type annotations match, because that
seems... unreasonable.

This would satisfy #9125 once all of the xfail markers are removed,
e.g., it checks that all keyword and positional arguments are
standardized.

…-project#10008)

Opening this in favor of ibis-project#9383 -- that PR also included all of the
breaking changes to unify function signatures and it was too much at
once. This PR adds only the signature checking mechanism, plus the
requisite xfails to lay out which inconsistencies are currently in Ibis.

## Motivation

We want to ensure that, for a given backend, that the argument names,
plus usage of positional, positional-only, keyword, and keyword-only
arguments match, so that there is API consistency when moving between
backends.

I've grabbed a few small parts of some of the utilities in Scott
Sanderson's
`python-interface` project
(https://github.com/ssanderson/python-interface).

While the upstream is no longer maintained, the goal of that project
aligns quite well with some of the issues we face with maintaining
consistent interfaces across backends.

Note that while the upstream project focused on _runtime_ enforcement of
these signatures matching, here it is only run in the test suite.

## Rough procedure

Any method that doesn't match can be skipped entirely (this is useful
for things like `do_connect`, which cannot reasonably be assumed to
match) or individually (by specifying a `pytest.param` and marking the
failing backends).

Then we scrape across the common parent classes and add any methods that
are NOT currently specified in the pre-existing xfailed ones. It's a bit
of a nuisance, but it's done, and ideally the manual listing of the
inconsistent methods goes away as we unify things.


I've opted for not checking that type annotations match, because that
seems... unreasonable.

This would satisfy ibis-project#9125 once all of the xfail markers are removed,
e.g., it checks that all keyword and positional arguments are
standardized.