Implemented support for Zarr-based multivec files and an HDF5-Zarr multivec converter

[conradbzura]

Description

What was changed in this pull request?

I've added Zarr support to the mutlivec tileset logic. It'll default to HDF5, but the option to read from Zarr is there.

Why is it necessary?

Zarr is a scalable array storage format that aligns nicely with the concept of a tileset. It should be more efficient to read Zarr than HDF5, particularly for large mutlivecs living on cloud-based object storage.

Fixes #162

Checklist

• Unit tests added or updated
• Updated CHANGELOG.md
• Run black .

[conradbzura]

My implementation adds a storage parameter to the tile getter functions (e.g., here). I could use some input as to how best to expose this to Higlass, however, as there is no way to pass extra arguments to the dynamically-generated "lazy clodius loader" currently. My thought would be to accept additional kwargs to the loader class somehow. Could sprinkle in some typing.ParamSpec magic to make it user friendly in an IDE, too.