Function sign_clob_auth 

pub fn sign_clob_auth(
    private_key: &EvmPrivateKey,
    timestamp: &str,
    nonce: u64,
) -> Result<(String, String)>

Signs a ClobAuth EIP-712 message for L1 API authentication.

Used to create or derive API credentials via the CLOB /auth/api-key and /auth/derive-api-key endpoints.

Returns (signer_address_hex, signature_hex).