Bitwise aggregations do not return scalar when called on Series

[orlp]

All aggregations when called directly on a Series should return a scalar, the bitwise_(and/or/xor) aggregations currently do not and incorrectly return a Series:

>>> pl.Series([1, 2]).sum()
3
>>> pl.Series([1, 2]).bitwise_or()
shape: (1,)
Series: '' [i64]
[
        3
]