add no grad to retrieval SentenceTransformer calls (#10494)

Author: puririshi98

torch_geometric/llm/utils/backend_utils.py

@@ -408,7 +408,8 @@ def apply_retrieval_via_pcst(
         :return: Retrieved graph/query data
         """
         # PCST relies on numpy and pcst_fast pypi libs, hence to("cpu")
-        q_emb = model.encode([query]).to("cpu")
+        with torch.no_grad():
+            q_emb = model.encode([query]).to("cpu")
         textual_nodes = [(int(i), full_textual_nodes[i])
                          for i in graph["node_idx"]]
         textual_nodes = DataFrame(textual_nodes,

torch_geometric/llm/utils/vectorrag.py

@@ -65,7 +65,8 @@ def query(self, query: Union[str, Tensor]) -> List[str]:
             List[str]: Documents retrieved from the vector database.
         """
         if isinstance(query, str):
-            query_enc = self.encoder(query, **self.model_kwargs)
+            with torch.no_grad():
+                query_enc = self.encoder(query, **self.model_kwargs)
         else:
             query_enc = query