Streamline Dask Imports

[aGuyLearning]

Description of feature

As of now we are duplicating the following:

if TYPE_CHECKING:
    from collections.abc import Collection

    from anndata import AnnData

try:
    import dask.array as da

    DASK_AVAILABLE = True
except ImportError:
    DASK_AVAILABLE = False

We should look into handeling this in a central location similar to the solution scanpy found.
Meaning we have a _compat.py file containing this logic and importing dask from there. So just one line. We could then throw an error, if a user tries to import dask