Backward prefetching: taus added from history are stride-independent!

[SalvatoreDiGirolamo]

When adding the taus from the simulation history, we should take only the ones that are relative to the client's stride. Instead, now we take the ones with the minimum stride (i.e., Delta d).

See:
https://github.com/SalvatoreDiGirolamo/SimFS/blob/d269be8c2a6807721eaeed444f6275a2fc2d9b7e/src/dv/server/ClientDescriptor.cpp#L158