Sc 4 multiple tables

[ArneDefauw]

• support for multiple tables in sparrow, as supported by spatialdata.
• io needed to be updated in sparrow, see https://github.com/scverse/spatialdata/discussions/520 and https://github.com/scverse/spatialdata/pull/525
• now user can use sparrow both for multiple samples and multi omics
• for analysing multiple samples, on can use append flag in sp.tb.allocate, andsp.tb.allocate_intensity, see e.g. https://github.com/saeyslab/harpy/blob/cb9bc66e39fc6cc08b4dfa1c5025a4e34c412b36/src/sparrow/_tests/test_table/test_allocation.py#L28

and

https://github.com/saeyslab/harpy/blob/cb9bc66e39fc6cc08b4dfa1c5025a4e34c412b36/src/sparrow/_tests/test_table/test_allocation_intensity.py#L15

• unit tests where added for some key functions related to spatial transcriptomics + added of test spatialdata object for spatial transcriptomics.