fix/nested shard reads

[d-v-b]

Fixes #3652 by properly allowing byte range requests in the partial decoding pathway of the sharding codec.

The failure was caused by a certain store-like class (defined just for sharding) failing to handle byte range requests.

There are 2 ways to fix this. One leaves a lot of the cruft in the sharding codec intact and just adds modifies some existing methods. But the other approach removes cruft, and re-uses stuff we have already defined elsewhere in the codebase: the Store API. That's what this PR does. Edit -- this PR now keeps the cruft, with the goal of keeping things small and simple.

In a later PR..., ShardingByteGetter and ShardingByteSetter can be removed, and instead the sharding codec creates Store classes as part of its decoding process. When reading a full shard, a _ShardReaderStore is created, which maps string keys (the names of chunks) onto contiguous ranges in a buffer (the shard bytes). When reading a partial shard, the separate chunk byte regions are used to create a MemoryStore.

Using the Store API here means nested sharding just works, and we get an easy way to add things like caching later.

[codspeed-hq]

Merging this PR will not alter performance

✅ 30 untouched benchmarks

---

_{Comparing d-v-b:fix/nested-shard-reads (19e0e0c) with main (4cddcf5)}

[d-v-b]

by making the shape of the array irregular w.r.t to the chunk shape, we hit the partial decode path, which required for evoking the bug reported in #3652

[d-v-b]

setting compressors to None here is also required to trigger the partial decode path.

[codecov]

Codecov Report

❌ Patch coverage is 34.61538% with 51 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.55%. Comparing base (7eba7f1) to head (e6784d7).

Files with missing lines	Patch %	Lines
src/zarr/codecs/sharding.py	34.61%	51 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3655      +/-   ##
==========================================
- Coverage   60.88%   60.55%   -0.34%     
==========================================
  Files          86       86              
  Lines       10182    10226      +44     
==========================================
- Hits         6199     6192       -7     
- Misses       3983     4034      +51     

Files with missing lines	Coverage Δ
src/zarr/codecs/sharding.py	51.67% <34.61%> (-10.44%)	⬇️

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