Make ObjectStore a generic class

[dstansby]

This makes ObjectStore generic with respect to the underlying store, mirroring similar structure in LoggingStore and WrapperStore. This allows type checkers to infer the type of the underlying store:

from typing import reveal_type

import obstore.store

from zarr.storage import ObjectStore

store = ObjectStore(obstore.store.MemoryStore())
reveal_type(store.store)
# Before: Revealed type is "Union[obstore.store.AzureStore, obstore.store.GCSStore, obstore.store.HTTPStore, obstore.store.S3Store, obstore.store.LocalStore, obstore.store.MemoryStore]"
# After:  Revealed type is "obstore.store.MemoryStore"

[d-v-b]

cc @kylebarron

[codecov]

Codecov Report

❌ Patch coverage is 14.28571% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 61.20%. Comparing base (48e7f4d) to head (ea18a1b).

Files with missing lines	Patch %	Lines
src/zarr/storage/_obstore.py	14.28%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3486      +/-   ##
==========================================
- Coverage   61.21%   61.20%   -0.01%     
==========================================
  Files          84       84              
  Lines        9923     9924       +1     
==========================================
  Hits         6074     6074              
- Misses       3849     3850       +1     

Files with missing lines	Coverage Δ
src/zarr/storage/_obstore.py	60.82% <14.28%> (-0.29%)	⬇️

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[kylebarron]

This is fine code-wise but why do you need to go back to the underlying object store once you've constructed the zarr store?

[dstansby]

I'm not 100% sure, but at least in the tests here in zarr-python the underlying store is accessed. My motiviation for this was fixing typing in our test suite here, so there may well not be a real world use case. Definitely happy to be guided by those who use/develop ObjectStore on whether this change is worth making or not.

As a related aside, if there is no need for users to access the underlying store would it be worth deprecating .store and renaming to ._store to signal that they shouldn't need to access it?

[kylebarron]

I think it's fine to add the generic. I don't think it exposes too much internal details.