[Proposal] Investigate and consider supporting failing signature verifications

[vicsn]

💥 Proposal

@HarukaMa noted: it seems some failed verification would reject the program right away instead of giving the program the freedom to process failures.

Typically we require developers to explicitly assert.eq r0 true/false to determine how to handle an operation's result.

[HarukaMa]

Discovered when the explorer was processing this tx: https://testnet.aleoscan.io/transaction?id=at142wxx8hxdcfhhrj2dn6ynmyasvpgszz2kxatl2uuxks786cs65zqch3hkv

The evaluate function returned error with message "signature error", which seems to come from library signature which is a dependency of ecdsa. Seems the library returned signature::Error() during the signature verification.