(fix): clarify public backed sparse docstring/api

[ilan-gold]

For #1598 (review)

Perhaps should go in separately to main as it is a cleaner git blame IMO

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

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.

Project coverage is 84.30%. Comparing base (94b2304) to head (94746c2).
Report is 67 commits behind head on main.

Files with missing lines	Patch %	Lines
src/anndata/_core/sparse_dataset.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1608      +/-   ##
==========================================
- Coverage   86.83%   84.30%   -2.54%     
==========================================
  Files          37       37              
  Lines        6016     6000      -16     
==========================================
- Hits         5224     5058     -166     
- Misses        792      942     +150     

Files with missing lines	Coverage Δ
src/anndata/_core/sparse_dataset.py	92.23% <87.50%> (-0.70%)	⬇️

... and 8 files with indirect coverage changes

[flying-sheep]

So you want us to commit to the whole API?

If not necessarily: There are ways to make users see only part of it, I can help with that.

[ilan-gold]

If not necessarily: There are ways to make users see only part of it, I can help with that.

Sorry went to lunch before getting to that. I made private what I thought should be, and left what I thought should be public as such. Feel free to comment otherwise

[flying-sheep]

Awesome! I don’t think we want people to manually initialize it, but I think not much harm is done if they try do do that.