[Wallet/Mint] Implement update to NUT-08: Dynamic amount of tokens for change

[callebtc]

Instead of using 4 blank outputs, we should use the new dynamic amount. Relates to following NUT update: cashubtc/nuts@1676fe8 which uses ceil(log2(fee_reserve)).

Todo:

• Mint
• Wallet
• Write test for wallet that checks expected returned fees?

[xphade]

I'd take this task in case no one else started yet.

[BilligsterUser]

I think i should be

ceil(log2(fee_reserve))||1

[xphade]

I think i should be

ceil(log2(fee_reserve))||1

@BilligsterUser You mean like "the minimum number of blank outputs should be 1"? Yeah, that probably makes sense.

[BilligsterUser]

Yes

[xphade]

@callebtc Can you weigh in on this as well? Should we add the minimum to NUT-08? If yes, I could make it part of my PR cashubtc/nuts#17.

[callebtc]

Correct, thank you for noticing this @BilligsterUser! If fee reserve is set to 1 sat minimum, this would fail.

I would write this as max(ceil(log2(fee_reserve)), 1) to be a bit more explicit maybe.

@xphade please feel free and go ahead with the fix of NUT-08 and also if you'd like to make appropriate changes to Nutshell!

[BilligsterUser]

cashubtc/nuts#20