BUG/EA: groupby on an EA should return the EA type
```
In [1]: df = pd.DataFrame({'Int': pd.Series([1, 2, 3], dtype='Int64'), 'A': [1, 2, 1]})
   ...: df
   ...: 
Out[1]: 
  Int  A
0   1  1
1   2  2
2   3  1

In [2]: df.groupby('A').Int.sum()
Out[2]: 
A
1    4
2    2
Name: Int, dtype: int64
```

[2] should be of type Int64; IOW this aggregation needs to be passed thru to the EA _from_sequence