Implement new coin selection algorithm (#301)

[sj-fisher]

This is an attempt at implementing a new coin selection algorithm to address #301. Feedback would be appreciated. Please see issue #301 for some notes on how this works and the thinking behind it.

This is a draft pull request because there is one test failure with this code which I would like some advice on (tests/test_wallet_restore.py:364).

[callebtc]

Hi there! As you might have noticed, the coin selection (I should call it output selection) algorithm has completely changed a few weeks ago. The wallet now selects outputs so that it has at least n of each amount available as a goal. The issue with many small values accumulating should have been fixed with that as well.

Have you had a chance to look at it yet? Here is the function that selects the outputs for a swap:

nutshell/cashu/wallet/wallet.py

Line 377 in 8af1b61

def split_wallet_state(self, amount: int) -> List[int]:

[sj-fisher]

Thanks, I hadn't seen that. Aiming to keep the same number of each denomination of coin in the wallet is a neat idea! Should I close this (and issue #301) or will you?