Account Config
data class AccountConfig(var directory: String, var relay: String, var accounts: String, var provisioning: String, var identifier: String, var device: UByte)
Where to reach a server's account endpoints, plus the credentials to sign in with. Addresses are host:port strings. Used by the account flow (Client.signIn), which signs in and provisions this device under the account's handle (e.g. acme/alice).