Add [partial_]decode_into API

[LDeakin]

Resolves a performance regression introduced in 0.16 when decoding sharded arrays with Array::[async_]retrieve_array_subset_opt.

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 28 lines in your changes missing coverage. Please review.

Project coverage is 82.96%. Comparing base (65542cc) to head (9d21650).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
zarrs/src/array/array_sync_readable.rs	90.00%	9 Missing ⚠️
zarrs/src/array/array_async_readable.rs	91.75%	8 Missing ⚠️
...ay/codec/array_to_bytes/sharding/sharding_codec.rs	93.45%	7 Missing ⚠️
zarrs/src/array/codec.rs	95.45%	3 Missing ⚠️
...arrs/src/array/codec/array_to_bytes/codec_chain.rs	98.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #75      +/-   ##
==========================================
+ Coverage   82.72%   82.96%   +0.23%     
==========================================
  Files         162      162              
  Lines       22228    22626     +398     
==========================================
+ Hits        18389    18771     +382     
- Misses       3839     3855      +16     

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