ETHSignature constructor
Creates an Ethereum signature from the 'r', 's', and 'v' components.
Throws a MessageException if the provided 'v' is not 27 or 28.
Implementation
ETHSignature(this.r, this.s, this.v) {
if (v != 28 && v != 27) {
throw MessageException("Invalid signature recovery id",
details: {"input": v});
}
}