(feat): zarr v3 guide

[ilan-gold]

• Closes #
• Tests added
• Release note added (or unnecessary)

Rendered

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 84.79%. Comparing base (6d9eb08) to head (1f25a0d).
Report is 36 commits behind head on main.

Files with missing lines	Patch %	Lines
src/anndata/_io/specs/methods.py	75.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1948       +/-   ##
===========================================
+ Coverage   24.85%   84.79%   +59.93%     
===========================================
  Files          46       47        +1     
  Lines        6904     6918       +14     
===========================================
+ Hits         1716     5866     +4150     
+ Misses       5188     1052     -4136     

Files with missing lines	Coverage Δ
src/anndata/_io/specs/methods.py	89.34% <75.00%> (+78.39%)	⬆️

... and 46 files with indirect coverage changes

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[flying-sheep]

Hi, the text is mostly great, nicely structured! I commented on the few cases where I got confused.

First of all it’s always nice when a PR is about 1-2 docs pages to provide links in your initial PR comment (“PR body”? I never know how to refer to that text box).

Something like

### [Rendered](https://icb-anndata--1948.com.readthedocs.build/en/1948/zarr-v3.html)

Please start using one sentence per line in markup documents, that way I can actually comment on what I want to comment on instead of one giant paragraph. I did it myself this time so I could comment.

Please also use typography:

• En-dashes: “–” (very easy to type on your MacBook: Alt/option+-)
• Times symbol: “×” (avoids confusion between AnnData.X and factors like “2×”)

[ilan-gold]

@flying-sheep I update the notebook a bit to use the new public data url and also added a note about obstore among some other minor cleanups.

[flying-sheep]

this is still broken:

[flying-sheep]

looks good apart from the broken syntax, please fix that before merging