Mod to stop playable sims being used by the game as food vendors

There's also Zero's Assign NPC mod.

I use NPCC to assign roles in my town, so I don't have any problems with vendors. I know NPCC is outdated and locked behind a paywall, so Zero has provided an alternative. They even have a No Random Townies, as well.

I do also use Lotharihoe's Sim Spawn Overhaul. It does have an option in the mod to have vendors only be homeless sims only.