Is there a straightforward way to add placement constraints, such as placing cells in specific/separate physical areas - or even doing something such as: “cells of type X must be some distance away from other cells of the same type”?

There aren't general constraints. You can manually place a cell at a fixed location. What is your use case?

I need to be able to keep flip flops spaced away from one another. This is for triple redundant logic, where I need the redundant DFF’s to be a minimum distance away from one another

Is there an example of placing cells at fixed locations? I'm going to need to do this shortly.

I see that we have the db apis but no simple user command. It wouldn't hard to add one