Reduced memory usage for SAG and SAGA

[MargaretDuff]

It is mentioned in passing in the original paper (in section 4), but section III.C) in the review https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=9226504, spells it out more clearly this should be applicable to both say CT and PET data fidelities (but might be more relevant for CT)

[MargaretDuff]

More clearly explained in algorithm 12 of https://arxiv.org/pdf/2406.06342