Change SchnorrVerify opcode to SchnorrRecoverSigner

[TomAFrench]

Problem

Similarly to #66, we're applying an eq constraint here which we can do in Noir.

Solution

Change SchnorrVerify Opcode to SchnorrRecoverSigner instead.

Alternatives considered

(Describe any alternative solutions you have considered.)

Additional context

(If applicable.)

[TomAFrench]

Seems like Schnorr signatures don't allow recovering the public key given the message similarly how you can with ECDSA signatures.