Add `Reserved` variant to `Address` and use it for chain address

[deuszx]

enum Address {
    Reserved(u16), // 0x + 4 low-case hex digits (e.g. chain balance 0x0000)
    Address32([u8; 32]), // 0x + 64 low-case hex digits (Sui, Linera)
    Address20([u8; 20]), // 0x + 40 low-case hex digits (Ethereum)
}

[Ehsanbad]

ok

[deuszx]

This is now done.