[Misc][V0 Deprecation] Add __main__ guard to all offline examples (#1837)

### What this PR does / why we need it?
Add `__main__` guard to all offline examples.

- vLLM version: v0.9.2
- vLLM main:
76b494444f

---------

Signed-off-by: shen-shanshan <467638484@qq.com>

examples/offline_inference_npu_tp2.py

@@ -25,7 +25,8 @@ os.environ["VLLM_WORKER_MULTIPROC_METHOD"] = "spawn"
 
 from vllm import LLM, SamplingParams
 
-if __name__ == "__main__":
+
+def main():
     prompts = [
         "Hello, my name is",
         "The president of the United States is",
@@ -48,3 +49,7 @@ if __name__ == "__main__":
         prompt = output.prompt
         generated_text = output.outputs[0].text
         print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")
+
+
+if __name__ == "__main__":
+    main()