Add rename functionality for stores.

[zoj613]

This adds the ability to rename either a group or array node in a Zarr hierarchy.

[codecov]

Codecov Report

Attention: Patch coverage is 98.14815% with 1 line in your changes missing coverage. Please review.

Project coverage is 98.12%. Comparing base (9f96f21) to head (53de8d5).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
zarr/src/storage/memory.ml	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #72      +/-   ##
==========================================
- Coverage   98.17%   98.12%   -0.05%     
==========================================
  Files          18       18              
  Lines        1312     1335      +23     
==========================================
+ Hits         1288     1310      +22     
- Misses         24       25       +1     

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