Add support for storage transformers.

[zoj613]

closes #24

[codecov]

Codecov Report

❌ Patch coverage is 44.73684% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.26%. Comparing base (aa31327) to head (dc2e1bf).
⚠️ Report is 124 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/extensions.ml	32.00%	17 Missing ⚠️
lib/metadata.ml	42.85%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #26      +/-   ##
==========================================
- Coverage   94.82%   93.26%   -1.57%     
==========================================
  Files          13       13              
  Lines        1082     1113      +31     
==========================================
+ Hits         1026     1038      +12     
- Misses         56       75      +19     

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[zoj613]

@d-v-b, Are there any storage transformers being used in practice for Zarr v3? The spec doesn't define any and I haven't seen any other implementation that uses them. I'd like to add one transformer to this PR but have no clue which practical transformer to support.

[d-v-b]

I'm not aware of any! Maybe you could start with an IdentityTransformer that essentially implements f(x) -> x as a placeholder, then add real transformers if / when people start using them?

[zoj613]

I'm not aware of any! Maybe you could start with an IdentityTransformer that essentially implements f(x) -> x as a placeholder, then add real transformers if / when people start using them?

That's essentially what i've done so far. I guess i'll just wait until the community starts using them. Thanks for the quick reply!