Simply don't ;), or if you must, use network namespaces* to make sure the torrent endpoint gets a different IP address than the twitch receiving application.
That said, there are ways to make this work, but for ingress traffic these require some pretty heroic measures that are not supported in sqm-scripts out of the box, have a look at https://forum.openwrt.org/t/ultimate-sqm-settings-layer-cake-dscp-marks-new-script/53209 for how to solve that issue. Note that the per-internal-IP fairness mode does not require this level of in direction, since cake can peek into the conntrack database to see the internal IP addresses, in a way that tc can not and hence all the trickery to get the cake shaper instantiated after iptables/nftables had a go at incoming packets.
Well, as I tried ot explain, this basically gives you by external IP-address fairness, might be fine, but since the external IP addresses are not under your control and not guaranteed to be static this is going to be a hit-and-miss heuristic. E.g. usually torrent requests come from other users most from a different external IP address, so what works well for your test (with probably just a few IP addresses in use by the measurement servers) might actually not work that well with real-life torrenting.
Well, you can also look at cake's estimates of delay, but the delay might already occur on the path to your router, so inside the internet cloud and completely out of your control.
*) I want to note that in theory that should work under Linux, but I zero first hand experience how to set that up, so please do not ask me how to do that 