I need to fix timestamp semantics after std.time.milliTimestamp was changed to a signed type. I need to fix zig test timing.zig.

Connection is initiated with a handshake. 8 bytes for the punch protocol magic value 0x8ec04ff4a00e8694, then 1-byte indicating which role the endpoint is taking. 0 for the initiator role which will be opening tunnels, and 1 for the forwarder role which will accept OpenTunnel messages and forward the tunnel data to another endpoint.

TODO: support authentication? Allow an authenticate command which requires a sequence of bytes to be sent from the other endpoint.