Add a command line option to disable upcasting in some cross attention ops.

main.py

@@ -6,6 +6,10 @@ import threading
 import queue
 import traceback
 
+if '--dont-upcast-attention' in sys.argv:
+    print("disabling upcasting of attention")
+    os.environ['ATTN_PRECISION'] = "fp16"
+
 import torch
 
 import nodes