RSV Signature Serialization
type RecoveryParam = number | null | undefined;
interface SignatureOptions {
r: BN;
s: BN;
recoveryParam: RecoveryParam;
}
function exportRecoveryParam(recoveryParam: RecoveryParam): string | null;
function importRecoveryParam(v: string): number | undefined;
function serializeSignature(sig: SignatureOptions): string;
function deserializeSignature(sig: string, size = 64): SignatureOptions;