I recently commented on a juniors code, and put in about four lines of code showing how I would improve the performance- but to do so I of course had to bring up a REPL and put the code in and run it and had more or less done a PR.
Make it faster and easier to inject and piece of code into the PR flow (branch pu?), make the whole code base simple to run from any point in memory, fully testrigged, so "just those highlighted lines" can be run and everyone can see.
What we are doing with this OP approach is making it easier for a human brain to imagine what the runtime will be like. That's the wrong approach - make it easier to have the runtime run over the chnaged lines of code and let people step through at PR time, and then make their changes alongside.
Or just leave a comment.
But we know what the rules are on comments on the internet