Small compatibility issues with SpatialData

[lopollar]

• Make sure the indices of the annData object are str and not int
• When reading to Dask, make the gene column of the transcript locations a categorical
• If no transformation is necessary, set transformation to identity and not to translation (0,0)

[ArneDefauw]

"Make sure the indices of the annData object are str and not int"

The indices of the anndata objects generated by SPArrOW are currently already 'str'.

[ArneDefauw]

saeyslab/harpy#70 fixes "When reading to Dask, make the gene column of the transcript locations a categorical".

Still need to merge it in sparrow