[feat] option to return csr tensors in datapipe

[martinkim0]

BREAKING CHANGE: replaces return_sparse_X argument with X_format that allows to specify the sparse format. default is kept to dense.

closes #617

[prathapsridharan]

@atolopko-czi @martinkim0 @pablo-gar - There has been no activity on the PR. Was this forgotten?

[atolopko-czi]

@atolopko-czi @martinkim0 @pablo-gar - There has been no activity on the PR. Was this forgotten?

It still needs to be reviewed & completed.

[ebezzi]

I'll do some cleanup to make sure the CI/CD is green and then I'll merge.

[github-actions]

This PR has not seen any activity in the past 4 weeks; if no one comments or reviews it in the next 3 days, this PR will be closed.

[prathapsridharan]

@ebezzi - note above automated message to close this PR. This comment serves to tell the automated closer to not close it :)

[github-actions]

This PR has not seen any activity in the past 4 weeks; if no one comments or reviews it in the next 3 days, this PR will be closed.

[github-actions]

This PR was closed because it has been inactive for 31 days, 3 days since being marked as stale. Please re-open if you still need this to be addressed.