Allow for Zarr stores being passed to ParticleFile

[willirath]

Let's allow for directly passing a zarr.storage.Store object to ParticleFile. This will allow for a couple of advanced output strategies:

• diskless capture of the output into a MemoryStore
• streaming data to a Redis store using RedisStore
• capturing output in a zip file using a ZipZtore (Possible but inefficient and throwing lots of warnings.)
• etc.

Todos:

• make sure ParticleFile works for Zarr stores directly.
• document changes
• add tutorial / example notebook with some of the above stores