Timed buffering is a bit trickier to test, more on that later
Sadly, the .merge tests still need to be fudged because of "Cannot call method 'more' on a null object"
Oddly enough, identical implementations of .zip and .merge work in the test, but not when they're pre-compiled in the settings. Go figure :-(
Made the zipping operator a named parameter (:with). This should allow later implementation of zipping N supplies rather than just 2
So at least we know the problem is in rakudo, not in the VM (most likely)
But found the reason. But no fix yet :-(