bs-45 WebTransport echo (forked h3)

Server: h3 + h3-webtransport from chaos-inc/h3, which now sends both the draft-02 0x2b603742 and the current-draft 0xc671706a settings and no longer demands a WebTransport setting back from the client. Same cert, same port, same page as the bs-42 wtransport control.

idle