(fix): remove read_elem_partial

[ilan-gold]

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.19%. Comparing base (ccfb6e3) to head (96fffaf).
⚠️ Report is 247 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1895      +/-   ##
==========================================
- Coverage   86.87%   85.19%   -1.69%     
==========================================
  Files          47       47              
  Lines        6912     6821      -91     
==========================================
- Hits         6005     5811     -194     
- Misses        907     1010     +103     

Files with missing lines	Coverage Δ
src/anndata/_io/specs/methods.py	95.85% <100.00%> (+5.90%)	⬆️
src/anndata/_io/specs/registry.py	94.28% <ø> (+0.04%)	⬆️

... and 5 files with indirect coverage changes