examples: add assistant-stream hello world example (#1000)

python/assistant-stream-hello-world/.gitignore

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+.vercel

python/assistant-stream-hello-world/api/chat/completions/index.py

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+from assistant_stream import create_run, RunController
+from assistant_stream.serialization import DataStreamResponse
+
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+import asyncio
+
+app = FastAPI()
+app.add_middleware(CORSMiddleware, allow_origins=["*"], allow_methods=["*"])
+
+
+@app.post("/api/chat/completions")
+async def chat_completions():
+    async def run(controller: RunController):
+        controller.append_text("Hello ")
+        await asyncio.sleep(1)
+        controller.append_text("world.")
+
+    return DataStreamResponse(create_run(run))

python/assistant-stream-hello-world/requirements.txt

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+assistant-stream==0.0.2
+fastapi==0.115.0