Support into_raw_fd for TcpStream to allow dispose but keep connection open

[utilitydelta]

What does this PR do?

Adds the ability to dispose of active TcpStream object but keep it open - for another executor to take over for example.

Motivation

I have a prototype server here that uses glommio: https://github.com/utilitydelta-io/glommio-sharded-affinity-server-starter

I wanted to migrate the tcp connection to a different executor.

Checklist

[x] I have added unit tests to the code I am submitting [x] My unit tests cover both failure and success scenarios