Turbopack: fix graph layout segment optimization (#77094)
The modules in the last layout segment (`server_component_entries`) were visited twice: as part of the last iteration of the for loop (which doesn't propagate its `visited_modules` because it's not a layout), and then again with `rsc_entry`.
We already do the right thing in another place:
https://github.com/vercel/next.js/blob/f42739d114695702922dab4c08d6c8223daafceb/crates/next-api/src/app.rs#L1740-L1748
Before:
After:
