arti SOCKS proxy: Tear down connections when client sends optimistic data

We do want to support optimistic data, see !2436 (comment 3081886)

However, right now, Arti risks mis-framing bugs if clients do send optimistic data, which would be quite serious.

Mitigates #1627 (closed) / TROVE-2024-010 by replacing the misframing bug with connection failure.

It doesn't seem so easy to write a test case for this.

This will conflict with !2436 (merged), but that's fine IMO. I'm going to assign review to @nickm since he wrote the original code here.

CC @dgoulet