Test from_zarr() methods on every group object

[dstansby]

Some of the tests we have aren't very 'end-to-end', in the sense that users will mostly interact with from_zarr(). It should be pretty easy to enhance existing tests by creating an in memory zarr group, then testing the from_zarr() methods on each OME-Zarr group in this package.

• HCS
• Image: Test Image.from_zarr() #117
• Labels: Replace remote labels test with local one #116
• ImageLabel: Fix image label parsing #113
• Well