Conditional profile scopes

[emilk]

Sometimes I find myself wishing there was a way to only instrument a piece of code if some condition is met, to reduce overhead:

fn do_stuff(n: usize) {
	puffin::profile_scope_if!(10_000 < n, "processing lots of data");
	for i in 0..n {
	    …
	}
}

If do_stuff is called once with a big n, we get a profile scope.
If do_stuff is called a million times with a small n, we don't pay the overhead of the profiling.