They mention the Nuclear Forces Treaty which manages to accomplish this for a similarly difficult problem, so i believe this is technicality a solvable problem, it's just a matter of political will.
I don't disagree that theoretically there could be some kind of test ban treaty type thing. But the mere fact that the primary rhetoric we see from leaders is around "winning the AI competition with China", I personally can't help but interpret this as a sign that nobody in the US is even close to ready to come to the table ready to slow things down.