Contract wallets incompatible with `EIP-1271` signature verification

The signature verification mechanism in IvSignerRecovery.sol relies exclusively on ECDSA recovery for validating signatures:

function _recoverSigner(
    SplitSig memory sig,
    uint256 iv,
    IStrategy strategy,
    uint256 maturityDate,
    uint256 relativeStrike
) internal view returns (address) {
    // Uses ECDSA recovery directly
    return _digest(iv, strategy, maturityDate, relativeStrike).recover(sig.v, sig.r, sig.s);
}

This implementation only supports signatures from Externally Owned Accounts (EOAs) and lacks compatibility with EIP-1271 (Standard Signature Validation Method for Contracts). As a result, users with smart contract wallets (such as Gnosis Safe) cannot use the protocol's option buying functionality in the OperationalTreasury.buy() function, because their contract-based signatures cannot be verified by ECDSA.recover.

With the growing adoption of smart contract wallets for enhanced security features and multi-signature capabilities, this limitation unnecessarily restricts the protocol's user base.

Extend the signature verification logic to support EIP-1271. This typically involves checking if the signer's address corresponds to a contract. If it is a contract, call its isValidSignature function to confirm the signature's validity according to the contract's own logic.