BUG: fix regression with SerieGrouper with Timestamp index (#42390)
closes https://github.com/pandas-dev/pandas/issues/42390

This fixes a regression introduced in c355ed1 where cache is not
initialized with correct state of islider and vslider.

On Timestamp index this trigger a "ValueError Length of values does not match length of index"
OK, I think the underlying problem here is that we shouldn't be getting to libreduction at all when we have a dt64tz DTI.  I think DatetimeIndex._has_complex_internals should be True for tzaware (possibly all of the datetimelike indexes, not totally sure) > OK, I think the underlying problem here is that we shouldn't be getting to libreduction at all when we have a dt64tz DTI. I think DatetimeIndex._has_complex_internals should be True for tzaware (possibly all of the datetimelike indexes, not totally sure)

see https://github.com/pandas-dev/pandas/issues/42390#issuecomment-888158663

 status here? needs a release note and IIUC @jbrockmendel prefers to fix the underlying issue https://github.com/pandas-dev/pandas/pull/42391#issuecomment-886911368

@jbrockmendel 1.3.2 scheduled for end of this week, can you take a look. (There are several open issues on 1.3.2 so I think will schedule 1.3.3 for 3 weeks after 1.3.2 so no pressure) The example in #42390 is fixed by changing DatetimeTimedeltaMixin._has_complex_internals to return True.  This will be a less-invasive alternative to ripping out SeriesBinGrouper which i expect we'll do for 1.4 closing this one as stale.