[python] Inconsistency in to_anndata density/sparsity of obsp/varp

[johnkerl]

While tiledbsoma.io.to_anndata() exports obsp/varp as a scipy.sparse matrix, ExperimentAxisQuery.to_anndata() exports it as a dense ndarray.

The AnnData API suggests the dense ndarray.

Update on #3362: @ivirshup points out that the AnnData docs are wrong and these should be sparse in all cases.

[sc-59632]

[ivirshup]

Oh let me clarify, it's not that it should be sparse in all cases. It's just that in the majority of cases it should be sparse. If the user really needs a dense array (maybe for a correlation matrix), they can do that.

Ideally you support both. I think the user would decide which they want by what format they stored it in.

[johnkerl]

Back to @bkmartinjr as discussed -- thanks @bkmartinjr ! :)