[WIP] Support for scipy.sparse.{csr,csc}_array

[ivirshup]

Starting support for scipy.sparse csc_array and csr_array. These are the new array-like interfaces for sparse matrices from scipy.

Fixes #746, #859

Still very WIP

TODO:

• [ ] Figure out compat with scipy<1.11
• [ ] Demo of how to load an array from disk
• [ ] Support for .X
• [ ] Tests (figure out which ones need adding)
• [ ] Fix concatenation tests
• [ ] Fix view tests
• [ ] Test for indices dtype after concatenation (e.g. #859)
• [ ] Release note

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 80.00000% with 25 lines in your changes are missing coverage. Please review.

Project coverage is 83.89%. Comparing base (0a768fc) to head (10ad4c9).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1028      +/-   ##
==========================================
- Coverage   84.18%   83.89%   -0.29%     
==========================================
  Files          35       35              
  Lines        5607     5675      +68     
==========================================
+ Hits         4720     4761      +41     
- Misses        887      914      +27     

Files	Coverage Δ
src/anndata/_core/index.py	93.24% <100.00%> (+0.04%)	:arrow_up:
src/anndata/_core/views.py	84.93% <100.00%> (+0.87%)	:arrow_up:
src/anndata/_io/specs/methods.py	88.00% <ø> (ø)
src/anndata/utils.py	84.12% <100.00%> (ø)
src/anndata/_core/anndata.py	84.71% <81.81%> (-0.12%)	:arrow_down:
src/anndata/_core/sparse_dataset.py	94.09% <85.71%> (-0.63%)	:arrow_down:
src/anndata/compat/__init__.py	81.73% <75.00%> (-1.60%)	:arrow_down:
src/anndata/_core/merge.py	82.72% <82.60%> (-0.20%)	:arrow_down:
src/anndata/tests/helpers.py	83.81% <63.15%> (-2.36%)	:arrow_down:

... and 2 files with indirect coverage changes

[ilan-gold]

• [x] backed sparse array (instead of matrix)

[ilan-gold]

Ok @ivirshup I think this is read for a review. This PR should only focus on the use of the object in the AnnData class and not on reading. That will come next, but here there is writing functionality (which made sense to me to put here)..

[ilan-gold]

The test failures are from "FAILED anndata/tests/test_backed_sparse.py::test_append_overflow_check[csr_array-zarr] - numpy.core._exceptions._ArrayMemoryError: Unable to allocate 16.0 GiB for a..." - we could xfail these as well, but it seems like since this works for matrix, maybe there's a bug here?

[flying-sheep]

sorry for the force push, VS code messed things up and I simply undid the mess to get a clean merge commit.

[ilan-gold]

No worries @flying-sheep - much appreciated!

[ilan-gold]

Demo of how to load an array from disk

Probably belongs in the follow up PR given that we did not implement that functionality here