Documentation Example: Task Polling

Since a lot of users might be coming here from a Celery background where it's common to submit a task and poll it's results, it'd be good to demonstrate this with the following, somewhere in the docs.

```python
import asyncio
import time

import dramatiq
from dramatiq.brokers.redis import RedisBroker
from dramatiq.middleware import AsyncIO
from dramatiq.results import Results
from dramatiq.results.backend import DEFAULT_TIMEOUT
from dramatiq.results.backends.redis import RedisBackend
from dramatiq.results.errors import ResultMissing, ResultTimeout
from quart import Quart, jsonify

class RedisBackendExt(RedisBackend):
def get_result_from_message_key(self, message_key, *, block=False, timeout=None):
if timeout is None:
timeout = DEFAULT_TIMEOUT

if block:
timeout = int(timeout / 1000)
if timeout == 0:
data = self.client.rpoplpush(message_key, message_key)
else:
data = self.client.brpoplpush(message_key, message_key, timeout)

if data is None:
raise ResultTimeout(message_key)

else:
data = self.client.lindex(message_key, 0)
if data is None:
raise ResultMissing(message_key)

return self.unwrap_result(self.encoder.decode(data))

backend = RedisBackendExt()
broker = RedisBroker(host='localhost', port=6379)
broker.add_middleware(Results(backend=backend))
broker.add_middleware(AsyncIO())
dramatiq.set_broker(broker)

app = Quart(__name__) # totally decoupled from dramatiq

@dramatiq.actor(store_results=True)
async def cut_granite_with_toothpick(enqueue_time: float):
print(f'{enqueue_time=}')
await asyncio.sleep(4)
return 'finally, the granite is cut...'

@app.get('/message/')
async def get_result(message_key):
result = backend.get_result_from_message_key(message_key)
return jsonify({'result': result}), 200

@app.get('/')
async def index():
enqueue_time = time.time()
message = cut_granite_with_toothpick.send(enqueue_time)
message_key = backend.build_message_key(message)
print(f'http://127.0.0.1:8000/message/{message_key}')
return jsonify({'message_key': message_key}), 202

if __name__ == '__main__':
app.run(host='127.0.0.1', port=8000, debug=True)

# run this with python3.13 test.py
# also run dramatiq --processes 2 --threads 2 test
```