use dask.array functions instead of numpy

[fneum]

I had hoped for some performance gains, but this is not so clear.

[euronion]

NB: Most of the dask functions you have changed are just calls to the same numpy functions using ufunc, see the "direct" entries here: https://docs.dask.org/en/stable/array-numpy-compatibility.html#compatibility-with-numpy-functions .

Changing does give a bit of consistency, I'm not opposed.