BUG: ExtensionArray.equals expects ExtensionArray.all to return a numpy.bool_
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#### Problem description

The current implementation of `ExtensionArray.equals` expects that the implementation of `ExtensionArray.all` always returns a numpy scalar, see https://github.com/pandas-dev/pandas/blob/942beba1e8f49c931b7c501bb1eec0e383313ac7/pandas/core/arrays/base.py#L741. If you don't use `numpy` as the backing memory store, I don't it is reasonable to stick to NumPy scalars here.

Instead, the method should unpack `numpy` scalars if necessary but passthrough otherwise.

Context: This appeared while running the unit tests with `fletcher` and `pandas`' master.