REF: simplify kwargs unpacking in resample (#41235)

Author: ivanovmg

pandas/core/resample.py

@@ -1046,11 +1046,9 @@ class _GroupByMixin(PandasObject):
 
     _attributes: list[str]  # in practice the same as Resampler._attributes
 
-    def __init__(self, obj, **kwargs):
+    def __init__(self, obj, parent=None, groupby=None, **kwargs):
         # reached via ._gotitem and _get_resampler_for_grouping
 
-        parent = kwargs.pop("parent", None)
-        groupby = kwargs.pop("groupby", None)
         if parent is None:
             parent = obj
 
@@ -1416,15 +1414,13 @@ def get_resampler(obj, kind=None, **kwds):
 
 
 def get_resampler_for_grouping(
-    groupby, rule, how=None, fill_method=None, limit=None, kind=None, **kwargs
+    groupby, rule, how=None, fill_method=None, limit=None, kind=None, on=None, **kwargs
 ):
     """
     Return our appropriate resampler when grouping as well.
     """
     # .resample uses 'on' similar to how .groupby uses 'key'
-    kwargs["key"] = kwargs.pop("on", None)
-
-    tg = TimeGrouper(freq=rule, **kwargs)
+    tg = TimeGrouper(freq=rule, key=on, **kwargs)
     resampler = tg._get_resampler(groupby.obj, kind=kind)
     return resampler._get_resampler_for_grouping(groupby=groupby)