canary: bump CPU max_slices to 4

128 Nemotron download workers OOM'd when packed onto a single
cpu-erapids node (256GB). Allow up to 4 CPU nodes so Iris can
spread workers across them.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: yonromai

lib/iris/examples/coreweave-canary.yaml

@@ -52,7 +52,7 @@ scale_groups:
         region: US-WEST-04A
         pool: cpu-erapids
     min_slices: 0
-    max_slices: 1
+    max_slices: 4
     priority: 50
     slice_template:
       num_vms: 1