[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_distributed_inference_npu.py

@@ -17,28 +17,37 @@
 # Adapted from vllm-project/vllm/examples/offline_inference/basic.py
 #
 
+import os
 from vllm import LLM, SamplingParams
 
-prompts = [
-    "Hello, my name is",
-    "The president of the United States is",
-    "The capital of France is",
-    "The future of AI is",
-]
+os.environ["VLLM_USE_MODELSCOPE"] = "True"
+os.environ["VLLM_WORKER_MULTIPROC_METHOD"] = "spawn"
 
-# Create a sampling params object.
-sampling_params = SamplingParams(max_tokens=100, temperature=0.0)
-# Create an LLM.
-llm = LLM(
-    model="Qwen/Qwen2.5-0.5B-Instruct",
-    tensor_parallel_size=2,
-    distributed_executor_backend="mp",
-    trust_remote_code=True,
-)
+def main():
+    prompts = [
+        "Hello, my name is",
+        "The president of the United States is",
+        "The capital of France is",
+        "The future of AI is",
+    ]
 
-# Generate texts from the prompts.
-outputs = llm.generate(prompts, sampling_params)
-for output in outputs:
-    prompt = output.prompt
-    generated_text = output.outputs[0].text
-    print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")
+    # Create a sampling params object.
+    sampling_params = SamplingParams(max_tokens=100, temperature=0.0)
+    # Create an LLM.
+    llm = LLM(
+        model="Qwen/Qwen2.5-0.5B-Instruct",
+        tensor_parallel_size=2,
+        distributed_executor_backend="mp",
+        trust_remote_code=True,
+    )
+
+    # Generate texts from the prompts.
+    outputs = llm.generate(prompts, sampling_params)
+    for output in outputs:
+        prompt = output.prompt
+        generated_text = output.outputs[0].text
+        print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")
+
+
+if __name__ == "__main__":
+    main()