add foreach backend test selection

Author: warner-benjamin

tests/config.py

@@ -57,6 +57,18 @@ def is_supported(self, device: DeviceType) -> bool:
             # Triton requires GPU/XPU
             if not (torch.cuda.is_available() or (hasattr(torch, "xpu") and torch.xpu.is_available())):
                 return False
+        if self == Backend.foreach:
+            # skip foreach on CPU
+            if device == DeviceType.cpu:
+                return False
+            # forach has limited support on MPS/XPU
+            if (hasattr(torch.backends, "mps") and torch.backends.mps.is_available()) or (
+                hasattr(torch, "xpu") and torch.xpu.is_available()
+            ):
+                return False
+            # foreach wors best on CUDA devices
+            if not torch.cuda.is_available():
+                return False
         return True