test: allow to select which backend(s) to run tests for

[MarcoGorelli]

From a request in rapidsai/cudf#17662 (comment)

I've also wanted this myself, sometimes I just want to quickly run the pandas tests without waiting for the much slower modin / dask ones. Currently the only way to do that is to uninstall modin and/or dask, but it would be really nice if we could do something like

pytest -m 'pandas,polars,pandas[pyarrow]'

[camriddell]

I was just wishing for this today as well! We will probably need to swap out the string comparisons in the tests for a structured object.

namedtuple("...", ["backend", "dtype", "eval_strategy"])

where

• backend is the dataframe library,
• dtype is numpy, numpy_nullable, pyarrow, ?
• eval_strategy: eager, lazy

Since I just added modin_pyarrow I need to go through and catch all of the if "pyarrow" in str(constructor) 😅