moq-sock

Socket and thread-per-core listener plumbing shared by the native MoQ runtimes (moq-tokio and moq-uring).

• bind: dual-stack UDP/TCP binding with grown socket buffers, and SO_REUSEPORT for worker-per-core groups (Linux-only, refused loudly elsewhere).
• shard: forming and steering a reuseport group by QUIC connection id. A shard::Group holds the port (probing and locking against a second same-UID group), fixes the member count, and hands out one Member per slot in index order. Binding a member yields an opaque claim, and completing the group with every claim attaches a classic-BPF filter before any socket is released for serving. The completed group retains every member socket, so dropping one serving handle cannot renumber the survivors. A Shard names the slot a member ended up in, and cid_prefix is the byte its issued ids lead with.
• cpu: pinning worker threads to cores.

This is infrastructure, not an entry point: build against moq-tokio or moq-uring, which own the worker groups formed from these pieces.