Improve tx dependency estimation

[MujkicA]

Currently, estimate_tx_dependencies initiates a simulation for every dependency it needs to resolve.

@segfault-magnet suggested:
To reduce the number of simulations performed, we can add a high number of variable outputs to the tx before simulation and then inspect it afterwards to see how many were used.

Additionally, we'll have to watch the tx size limit. We can only add so many variable outputs until the limit is reached, then if the tx still reverts with missing outputs we have to communicate that there is no way of constructing a valid transaction.