Built a Multipath VPN using XQUIC

[mp0rta]

Hi xquic maintainers,

I built mqvpn, an open-source L3 VPN on top of xquic.

• mqvpn: https://github.com/mp0rta/mqvpn
• xquic fork: https://github.com/mp0rta/xquic/tree/feature/masque

I added MASQUE CONNECT-IP (RFC 9484) to xquic and built a VPN layer that tunnels IP packets over QUIC Datagrams with multipath support.

I also wrote a new multipath scheduler (WLB) designed for datagrams:

• Benchmark: https://github.com/mp0rta/mqvpn/blob/main/docs/benchmarks_netns.md#2-bandwidth-aggregation--wlb-vs-minrtt
• Implementation: https://github.com/mp0rta/xquic/blob/feature/masque/src/transport/scheduler/xqc_scheduler_wlb.c

I'd like to upstream the MASQUE and scheduler work, but the diff is large. What's the preferred way — multiple small PRs? If so, how would you like them split or feature-gated?

Thanks!