feat: add counts to pbmc68k_reduced

[flying-sheep]

Beyond time to actually have some raw count data.

TODO:

• move into dataset, maybe remove log_counts layer.
• maybe patch single mismatched number: we have 4.02, original (adata['AACTCACTGGGTGA-5', 'FTL']) could be restored via adata.X[357, 715] = 4.019 (4.0195003... is at the rounding boundary).
• remove version guards superseded by bumped versions

---

• Closes #
• Tests included or not required because:

• Release notes not necessary because:

[codecov]

Codecov Report

❌ Patch coverage is 95.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.10%. Comparing base (0a3ed86) to head (b0f97f8).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/scanpy/datasets/_datasets.py	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4269      +/-   ##
==========================================
+ Coverage   79.04%   79.10%   +0.06%     
==========================================
  Files         128      128              
  Lines       13412    13398      -14     
==========================================
- Hits        10602    10599       -3     
+ Misses       2810     2799      -11     

Flag	Coverage Δ
hatch-test.low-vers	77.34% <95.00%> (+0.09%)	⬆️
hatch-test.pre	78.98% <95.00%> (+0.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/scanpy/__init__.py	100.00% <100.00%> (+3.44%)	⬆️
src/scanpy/preprocessing/_pca/_compat.py	100.00% <100.00%> (ø)
src/scanpy/readwrite.py	82.60% <100.00%> (+1.57%)	⬆️
src/scanpy/tools/_louvain.py	100.00% <ø> (ø)
src/scanpy/datasets/_datasets.py	91.50% <92.85%> (+1.22%)	⬆️

... and 2 files with indirect coverage changes