Select Spendable Streamlined

[fluidvanadium]

This is a rewrite of select_spendable_notes, using what we have learned over the past couple of weeks.

Notable improvement is that the ignore_dust test goes from passing to failing for zip317

[zancas]

I left some notes.

[Oscar-Pepper]

I have left some comments which i think are worth implementing but non-blocking. The reason why I am requesting changes is because our expected fees seem to just be inputted by the test writer with no real reviewed expected fee calculator and some of the expected fees seem like they might be wrong to me. ALSO the new select_spendable_notes has lost control of selecting notes based on pool which i think is more important than value as it effects our pool policies and also is needed to reduce fees for user. although I havent worked out how this is even possible with the current LRZ code as the use_orchard / use_sapling booleans dont seem to work correctly or get fed into this function, so non-blocking... maybe we should implement this soon though.

[Oscar-Pepper]

wonderful