feat: add long context example (#6391)

scripts/playground/long_context_example.py

+from urllib.request import urlopen
+
+from openai import OpenAI
+
+test_cases = {
+    "64k": "https://qianwen-res.oss-cn-beijing.aliyuncs.com/Qwen2.5-1M/test-data/64k.txt",
+    "200k": "https://qianwen-res.oss-cn-beijing.aliyuncs.com/Qwen2.5-1M/test-data/200k.txt",
+    "600k": "https://qianwen-res.oss-cn-beijing.aliyuncs.com/Qwen2.5-1M/test-data/600k.txt",
+    "1m": "https://qianwen-res.oss-cn-beijing.aliyuncs.com/Qwen2.5-1M/test-data/1m.txt",
+}
+
+client = OpenAI(api_key="EMPTY", base_url="http://127.0.0.1:30000/v1")
+
+for name, url in test_cases.items():
+    print(f"\n==== Running test case: {name} ====")
+    try:
+        with urlopen(url, timeout=10) as response:
+            prompt = response.read().decode("utf-8")
+    except Exception as e:
+        print(f"Failed to load prompt for {name}: {e}")
+        continue
+
+    try:
+        response = client.chat.completions.create(
+            model="meta-llama/Llama-4-Scout-17B-16E-Instruct",
+            messages=[{"role": "user", "content": prompt}],
+            stream=True,
+            max_tokens=128,
+            temperature=0,
+        )
+
+        for chunk in response:
+            if chunk.choices and chunk.choices[0].delta.content is not None:
+                print(chunk.choices[0].delta.content, end="", flush=True)
+    except Exception as e:
+        print(f"\nError during completion for {name}: {e}")