Revise optimisation in balancing #500
Description
Currently, balancing minimized the distance between the value to reach and the set of UTxOs picked to reach it, provided that difference can fit within a change UTxO. This seems reasonable, but in fact, maybe it should be optimized simply in term of the number of input UTxOs.
We should conduct an analysis on the size of various transactions based on various possible sets of balancing UTxO, and decide how to proceed, as in the end, what is important is to minimize transaction size to decrease fees.
The balancing could also be improved by keeping in mind the set of candidate UTxOs when trying to optimise the fees.