go/neo/neonet: tests: Introduce T

This represents a neonet testing environment and in the future will be
used to run tests under different protocol versions, protocol encodings, etc.

For now it is noop wrapper around testing.T + t.bin that wraps []byte
and will be amended to return something different depending on t's
encoding.

go/neo/neonet/newlink_test.go

@@ -43,6 +43,9 @@ func _xhandshakeServer(ctx context.Context, c net.Conn, version uint32) {
 }
 
 func TestHandshake(t *testing.T) {
+	Verify(t, _TestHandshake)
+}
+func _TestHandshake(t *T) {
 	bg := context.Background()
 	// handshake ok
 	p1, p2 := net.Pipe()