pingserver-rs: use new-type pattern to capture session/stream metrics centrally

[brayniac]

Use the new-type pattern to wrap the TcpStream to get TCP metrics even when TLS is in-use. Also verify that writes to the session are being tracked properly so we can see logical bytes and actual bytes written-to/read-from the sockets

[brayniac]

This was addressed in #312 by the TcpStream type used in the session crate.