Cashu: handle pending proofs

[rolznz]

Currently it's possible if a payment got stuck to be unable to make any more payments.

1. Upgrade gonuts dependency: build(deps): bump github.com/elnosh/gonuts from 0.2.0 to 0.3.0 #776

2. Handle pending proofs: wallet - method to check state of pending proofs elnosh/gonuts#88

3. More clearly mark that this LNClient option is experimental in the onboarding

4. Consider a way for users from <0.3 to recover their funds as recommended by elnosh. But it must be isolated to the cashu LNClient. Maybe there could be some check at startup that if it discovers there are pending proofs it can reset the wallet?

[itstomekk]

There is one quite active Cashu discord server, great guys, I posted it there