Refactor model ID handling and tie weights in app.py

app.py

@@ -43,6 +43,7 @@ def load_model_a(model_id):
             device_map="auto",
             trust_remote_code=True,
         ).eval()
+    model_a.tie_weights()
     return gr.update(label=model_id)
     
 def load_model_b(model_id):
@@ -66,6 +67,7 @@ def load_model_b(model_id):
             device_map="auto",
             trust_remote_code=True,
         ).eval()
+    model_b.tie_weights()
     return gr.update(label=model_id)
 
 @spaces.GPU()