test: Rework how the OCaml listening port is passed to SC

Instead of passing the OCaml listening port as the first argument in the
OSC packet, write it as raw bytes to a file at test.data, and then read
the file in SuperCollider.

This enables us to test specific messages, rather than having to add an
argument to each test message.

Signed-off-by: John Else <john.else@citrix.com>
test: Add an extra test packet

This test packet is a message with Int32, Float32 and String arguments,
but no blobs. SuperCollider seems to have problems with blobs, so this
lets us test all the other argument types.

Signed-off-by: John Else <john.else@citrix.com>