chore: use scverse-misc for data downloading

[flying-sheep]

Not using the anndata loader here since

1. we use datasetdir and not a global cache … maybe we should get rid of that.
2. we use the fallback_urls inspired by SnapATAC2 – maybe that should be added to upstream @timtreis @ilia-kats?

---

• Closes Use scverse-misc for dataset downloading #4309
• Tests included or not required because:

• Release notes not necessary because:

[codecov]

Codecov Report

❌ Patch coverage is 91.11111% with 4 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@9e259ff). Learn more about missing BASE report.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/scanpy/io/_read.py	66.66%	2 Missing ⚠️
src/scanpy/datasets/_datasets.py	90.00%	1 Missing ⚠️
src/scanpy/datasets/_utils.py	95.83%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4310   +/-   ##
=======================================
  Coverage        ?   80.01%           
=======================================
  Files           ?      133           
  Lines           ?    13372           
  Branches        ?        0           
=======================================
  Hits            ?    10699           
  Misses          ?     2673           
  Partials        ?        0           

Flag	Coverage Δ
hatch-test.low-vers	77.93% <91.11%> (?)
hatch-test.pre	79.88% <91.11%> (?)

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

Files with missing lines	Coverage Δ
src/scanpy/_utils/__init__.py	75.57% <ø> (ø)
src/scanpy/io/_download.py	94.73% <100.00%> (ø)
src/scanpy/datasets/_datasets.py	92.02% <90.00%> (ø)
src/scanpy/datasets/_utils.py	96.96% <95.83%> (ø)
src/scanpy/io/_read.py	80.59% <66.66%> (ø)

[ilia-kats]

Looks good to me, but see scverse/scverse-misc#75.