TLV: better impl and a separate crate

[alexpyattaev]

Problem

• Alpenglow team wants to use TLV to encode alpenglow vote messages
• Existing TLV implementation in Gossip is not ideal and has some performance issues due to double handling of same bytes by bincode

Summary of Changes

• Isolate TLV into own crate
• Make parsers use Bytes where possible to minimize bugs

Still ToDo:

• hook the new impl into gossip