fix: calculate-actual-storage.ts can be improved.

[SgtPooki]

From @rvagg on slack:

FYI re upload size accounting (#276) you do have the option of taking the super-quick route if you want, and I think you might be able to do it in a way that doesn’t lose functionality:

1. Get clientDataSetIds from FWSS
2. For each data set, in parallel, get dataSetLeafCount from PDPVerifier - then you have the total byte size for a data set

• OR if you still want per-piece information, PDPVerifier has a pieceLeafCounts that you can get per data set — or maybe even better, there is a pieceCids per data set that you can get with a single call

We could put calls for these on PDPVerifier in Synpase if we don’t have them already.