Introduce dimension chunking check

[ArthurVincentCS]

Introduce the function

def is_dimension_chunked(da: Union[xr.DataArray, xr.Dataset], dim: str):
    """
    Check if a dimension of an xarray DataArray or Dataset is chunked.

    Parameters
    ----------
    da : xarray.DataArray or xarray.Dataset
        The object to check.
    dim : str
        The name of the dimension to check.

    Returns
    -------
    bool
    """
    ...  

Can be used everywhere needed.