Add dill support for enp typings

[copybara-service[bot]]

Add dill support for enp typings

Currently, running some functions on Apache Beam leads to errors.

This can be boiled down to this piece of code not working:

import dill
from etils.enp.typing import ui8
dill.dumps(ui8['N'])
>> PicklingError: Can't pickle ui8[N]: it's not found as etils.enp.array_types.typing.ui8

Additionally, if dill is not available, the behavior doesn't change.