Refactor codec metadata and fill values

[LDeakin]

This is a massive refactor, but should not be particularly impactful to users besides codec metadata moving to a new module.

zarrs_metadata

• Move all codecs into a new codec module
  • zarrs_metadata no longer distinguishes Zarr V2/V3 codecs within the v2/v3 modules
  • Zarr V2/V3 codec aliasing is handled in zarrs
• Add zfpy codec metadata (unmerging zfpy/zfp)
  • Remove write_header from zfp codec configuration (since zfpy is now separate)
• Refactor FillValueMetadataV3 to support arbitrary fill value metadata for ZEP0009

zarrs

• Change the default vlen codecs to vlen-utf8 / vlen-bytes instead of experimental vlen
• Refactor codec name handling and CodecTraits in alignment with ZEP0009 and the zarr-extensions repository
  • All "experimental" codecs now use the zarrs. prefix (or numcodecs. if fully compatible) instead of a URL
  • Add support for aliased codec names
• Improve the codec docs

Closes #116
Closes #125

[codecov]

Codecov Report

Attention: Patch coverage is 86.24161% with 205 lines in your changes missing coverage. Please review.

Project coverage is 81.91%. Comparing base (74bee58) to head (27eb79e).
Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
.../array_to_bytes/sharding/sharding_codec_builder.rs	30.61%	34 Missing ⚠️
zarrs/src/array/codec/options.rs	32.25%	21 Missing ⚠️
zarrs/src/config.rs	34.78%	15 Missing ⚠️
...ay/codec/array_to_array/bitround/bitround_codec.rs	33.33%	14 Missing ⚠️
...ay/codec/bytes_to_bytes/gdeflate/gdeflate_codec.rs	33.33%	14 Missing ⚠️
...arrs/src/array/codec/array_to_bytes/codec_chain.rs	89.36%	10 Missing ⚠️
...rs/src/array/codec/array_to_bytes/zfp/zfp_codec.rs	71.42%	10 Missing ⚠️
zarrs_metadata/src/v3/array/fill_value.rs	94.65%	10 Missing ⚠️
zarrs_metadata/src/codec_map.rs	62.50%	9 Missing ⚠️
zarrs_metadata/src/v2_to_v3.rs	85.96%	8 Missing ⚠️
... and 20 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #157      +/-   ##
==========================================
- Coverage   81.98%   81.91%   -0.07%     
==========================================
  Files         177      179       +2     
  Lines       25048    25522     +474     
==========================================
+ Hits        20535    20907     +372     
- Misses       4513     4615     +102     

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