When an Avalanche proof is loaded from a file or a hex string, we previously didn't attempt to look for the stakes in the current wallet. So when the stake commitment data (expiration timestamp, master pubkey) changed, we didn't update the stake signatures and they were shown as the originally loaded, now invalid, sigs.

Do a best effort attempt to find the corresponding address for an stake's outpoint in the current wallet, so that we update the signature when "Generate proof" is clicked.

This will only succeed for stake that belong to the wallet, and only if the wallet knows this outpoint (i.e. is not an offline wallet).

Generate a proof. Save it to a file. Load the proof from file. Change the expiration date. Generate the proof and see that the signature is updated and shows as valid (blue)