Refactor:Improve the float compare for LocalAIRerank (#9428)

### What problem does this PR solve?
Improve the float compare for LocalAIRerank

### Type of change

- [x] Refactoring

rag/llm/rerank_model.py

@@ -268,7 +268,7 @@ class LocalAIRerank(Base):
         max_rank = np.max(rank)
 
         # Avoid division by zero if all ranks are identical
-        if max_rank - min_rank != 0:
+        if not np.isclose(min_rank, max_rank, atol=1e-3):
             rank = (rank - min_rank) / (max_rank - min_rank)
         else:
             rank = np.zeros_like(rank)