feat(client) Make the ProducerFactory depend on a protocol

[markstory]

Using a concrete return type for ProducerFactory is blocking the adoption of a singleton producer in sentry.

Refs getsentry/sentry#111191

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

Bugbot Autofix prepared a fix for the issue found in the latest run.

• ✅ Fixed: Incomplete protocol migration leaves registry using concrete type
  • Updated TaskNamespace to use ProducerProtocol instead of KafkaProducer in _producers dict and _producer method return type, completing the protocol migration.

Or push these changes by commenting:

@cursor push e9348a2be7

Preview (e9348a2be7)

diff --git a/clients/python/src/taskbroker_client/registry.py b/clients/python/src/taskbroker_client/registry.py
--- a/clients/python/src/taskbroker_client/registry.py
+++ b/clients/python/src/taskbroker_client/registry.py
@@ -17,7 +17,7 @@
 from taskbroker_client.retry import Retry
 from taskbroker_client.router import TaskRouter
 from taskbroker_client.task import ExternalTask, P, R, Task
-from taskbroker_client.types import ProducerFactory
+from taskbroker_client.types import ProducerFactory, ProducerProtocol
 
 logger = logging.getLogger(__name__)
 
@@ -51,7 +51,7 @@
         self.default_processing_deadline_duration = processing_deadline_duration  # seconds
         self.app_feature = app_feature or name
         self._registered_tasks: dict[str, Task[Any, Any]] = {}
-        self._producers: dict[str, KafkaProducer] = {}
+        self._producers: dict[str, ProducerProtocol] = {}
         self._producer_factory = producer_factory
         self.metrics = metrics
 
@@ -191,7 +191,7 @@
             except Exception:
                 logger.exception("Failed to wait for delivery")
 
-    def _producer(self, topic: str) -> KafkaProducer:
+    def _producer(self, topic: str) -> ProducerProtocol:
         if topic not in self._producers:
             self._producers[topic] = self._producer_factory(topic)
         return self._producers[topic]

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