[BUG] Cellxpose returns 400 Bas request for some requests if data is 16-bit

Describe the bug

Try saving test file after converting to fp16:

adata.X = adata.X.astype('float16')

Server normally starts when given this data (but prints some warnigns about conversion from 64bits).

However when you select gene or run differential expression, 400 appears.

Version affected: 0.17.0, within docker

In my case cellxgene first downloads file from the cloud, so 16bit format for storage is very reasonable - almost halves the space.

[blrnw3]

Fixed in 1.0.1

[bkmartinjr]

Suggest a cast in diffex code if the set1/set2 slices are fp16, as that is where the dependency lives. Pretty sure the rest of the code base does not have this constraint.

As it is already sliced out of the main matrix, you will retain most of the memory savings (ie, the cast to 32 bit will be only for the duration of the t-test compute)