Mdurant v3 fsspec

[d-v-b]

Adds an instance of StoreTests parametrized by RemoteStore, and refactors the store tests layout

Not mergeable until we figure out why the tests are failing

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/tutorial.rst
• Changes documented in docs/release.rst
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[d-v-b]

@martindurant can you approve the workflows so we can see some test failures? that's the part I need help with :)

[martindurant]

I see no test failures :)