Add support for `DelayedMatrix`

[mfansler]

Using gChromVAR with a SummarizedExperiment that is backed by an HDF5Array (a DelayedArray implementation) can result in sending a DelayedMatrix object to some of the helper functions here (for example from here).

I believe it should be relatively straightforward to provide support for this, since it should be a matter of directing to use the DelayedMatrix implementations of colSums, rowSums in the helper_functions.R.