feat: new holoviz plotting

[flying-sheep]

TODO

• dotplot and so on
• other backends demo
• selenium for export
• re-export A/AdDim, …
• example notebook(s)

---

• Closes Holoviz based plotting #2656
• Tests included or not required because:

• Release notes not necessary because:

[codecov]

Codecov Report

❌ Patch coverage is 47.38220% with 201 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.55%. Comparing base (ecec3c2) to head (30cbbc7).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/scanpy/plotting/_v2/_core.py	0.00%	119 Missing ⚠️
src/scanpy/plotting/_v2/_tl.py	0.00%	44 Missing ⚠️
src/scanpy/plotting/_v2/_pp.py	0.00%	17 Missing ⚠️
src/scanpy/plotting/legacy/mpl_settings.py	89.23%	7 Missing ⚠️
src/scanpy/plotting/_v2/__init__.py	0.00%	5 Missing ⚠️
src/scanpy/datasets/_datasets.py	57.14%	3 Missing ⚠️
src/scanpy/plotting/__init__.py	89.47%	2 Missing ⚠️
src/scanpy/tools/_embedding_density.py	60.00%	2 Missing ⚠️
src/scanpy/plotting/legacy/_utils.py	87.50%	1 Missing ⚠️
src/scanpy/tools/_dendrogram.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4188      +/-   ##
==========================================
- Coverage   79.85%   78.55%   -1.31%     
==========================================
  Files         121      127       +6     
  Lines       12924    13141     +217     
==========================================
+ Hits        10321    10323       +2     
- Misses       2603     2818     +215     

Flag	Coverage Δ
hatch-test.low-vers	77.68% <47.38%> (-1.30%)	⬇️
hatch-test.pre	78.47% <47.38%> (-1.34%)	⬇️

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	96.55% <100.00%> (ø)
src/scanpy/_settings/__init__.py	96.11% <ø> (+4.38%)	⬆️
src/scanpy/external/pl.py	29.21% <100.00%> (ø)
src/scanpy/external/pp/_mnn_correct.py	22.22% <ø> (ø)
src/scanpy/plotting/_common.py	100.00% <100.00%> (ø)
src/scanpy/plotting/legacy/__init__.py	100.00% <100.00%> (ø)
src/scanpy/plotting/legacy/_anndata.py	85.42% <100.00%> (ø)
src/scanpy/plotting/legacy/_baseplot_class.py	80.36% <100.00%> (ø)
src/scanpy/plotting/legacy/_docs.py	100.00% <100.00%> (ø)
src/scanpy/plotting/legacy/_dotplot.py	91.89% <100.00%> (ø)
... and 21 more

... and 1 file with indirect coverage changes