Feature: Serde and/or Borsh support for TargetAddr

[void-ripper]

While not of life threatening importance, man that would be neat.

[RoKu1]

will pick this up

[sticnarf]

I'm inclined not to add such supports to TargetAddr.

The main purpose of having this type is to simulate method overloading, so Socks5Stream::connect can handle different types of targets.

I don't expect a TargetAddr to be (de)serialized. If you want to (de)serialize a target, just use a string for that.