dask deterministic hashing

[crusaderky]

sparse.COO should implement dask deterministic hashing:
https://docs.dask.org/en/latest/custom-collections.html#deterministic-hashing

The current situation is that dask falls back on a random uuid4:

>>> import dask.array
>>> import numpy
>>> import sparse
>>> a = numpy.array([1,2])
>>> sa = sparse.COO(a)
>>> dask.array.from_array(a).__dask_keys__()
[('array-de932becc43e72c010bc91ffefe42af1', 0)]
>>> dask.array.from_array(a).__dask_keys__()                                                                                                                                                                                                              
[('array-de932becc43e72c010bc91ffefe42af1', 0)]
>>> dask.array.from_array(sa).__dask_keys__()                                                                                                                                                                                                              
[('array-77964bd4315f9a3eb43953586a91d273', 0)]
>>> dask.array.from_array(sa).__dask_keys__()                                                                                                                                                                                                             
[('array-cf0d4b78cf3a2b277c351ea3d534a790', 0)]

Suggested implementation:

class COO:
    def __dask_tokenize__(self):
        from dask.base import normalize_token
        return normalize_token((type(self), self.coords, self.data, self.shape, self.fill_value))

[hameerabbasi]

Feel free to make a PR.

[danielballan]

Is anyone working on this already? If not, I'd be happy to make that PR. The implementation suggested about looks right to me.

[hameerabbasi]

Feel free. Thanks a lot for offering to contribute, it's really welcome.