Add MPS Fallback to support Torchtune Multimodal MPS (#1241)

Author: Jack-Khuu

torchchat.py

@@ -9,6 +9,11 @@
 import subprocess
 import sys
 
+# MPS ops missing with Multimodal torchtune
+# https://github.com/pytorch/torchtune/issues/1723
+import os
+os.environ["PYTORCH_ENABLE_MPS_FALLBACK"] = "1"
+
 from torchchat.cli.cli import (
     add_arguments_for_verb,
     arg_init,