EIP-1271 Signature Validator

Wallet signatures and smart account signatures are verified in completely different ways — one recovers a key, the other asks the contract — and this works out which applies before doing the right one. It checks both the current EIP-1271 interface and the pre-standard variant some deployed accounts still use, because checking only the modern one reports those as invalid. Messages are hashed the way personal_sign does, with its prefix, since verifying against the raw hash instead is the single most common reason a perfectly good signature appears broken. High s values are flagged, because such a signature has a valid mirror image and contracts that do not reject it can be replayed with the twin.