Fix import failing when using "python -OO"

[jsignell]

• Tests added / passed
• Passes black dask / flake8 dask
• Fixes importing fails when calling python -OO #6296

cc @dask/maintenance

To test: try python -OO -c 'import dask.array' on this branch vs master.

[martindurant]

?? optimised functions don't have names ?? :)

So you think it's worth doing a test run for OO, or at least an import check?

[jcrist]

We used to do this, but stopped since not many people wanted it and it took up a test matrix slot. The code logic is still in our travis setup, it's just not enabled.

[jsignell]

I think it's more like optimized partial functions don't have names. I think this PR is an improvement as I don't think the name is as intended on master anyways:

>>> import dask.array
>>> print(dask.array.full.__name__)
blocked_full

don't really care one way or the other about CI.

[martindurant]

OK :)