What problem does this feture solve?

Currently, privatekey, xpriv, xpub cannot be initialized.

Describe what you've considered?

Code sample / Spec

    public init(_ base58: Base58Check) throws {
        guard let raw = Base58.decode(base58) else {
            throw AddressError.invalid
        }
        let checksum = raw.suffix(4)
        let pubKeyHash = raw.dropLast(4)