`var_by_distance` using polygons annotations

proposed signature

def var_by_distance(
    sdata: SpatialData,
    groups: str | list[str] | NDArrayA,
    cluster_key: str,

    library_key: str | None = None, # only anndata
    metric: str = "euclidean", # if annotations is not None, this doesn't apply
    spatial_key: str = "spatial",

    annotations: str | list[str] | None = None, # shapes key
    annotation_mask: str | None = None, # negative mask for distances to annotations
    coordinate_system: str  | None = None, # check which cs wrt annotations

    design_matrix_key: str = "design_matrix",
    covariates: str | list[str] | None = None,
    
    copy: bool = False,
    )

@LLehner