Make Verifier trait instance-based

[vaporif]

Description

Convert the Verifier trait from static methods to instance methods to enable stateful signature verification.

Use case: In Solana's IBC v2 implementation, transaction verification must be offloaded outside the main transaction context. An instance-based verifier allows referencing an accessor that checks verification results asynchronously.

Definition of "done"

Change:
// Before
fn verify(pubkey: PublicKey, msg: &[u8], signature: &Signature) -> Result<(), Error>;

// After

fn verify(&self, pubkey: PublicKey, msg: &[u8], signature: &Signature) -> Result<(), Error>;

Implementation is already complete and tested in our Solana IBC implementation. Awaiting approval to submit PR.