Rename BaseTask → BaseWorker and reserve "task" for asyncio

Replaces every "task" identifier that referred to the BaseTask
abstraction with "worker". Asyncio task plumbing (asyncio.Task,
BaseTaskManager, TaskManager, create_task, cancel_task, etc.) stays
untouched. Highlights:

- Classes: BaseTask → BaseWorker, PipelineTask → PipelineWorker,
  LLMTask → LLMWorker, LLMContextTask → LLMContextWorker, TaskBus →
  WorkerBus, TaskRegistry → WorkerRegistry, TaskActivationArgs →
  WorkerActivationArgs, TaskReadyData → WorkerReadyData,
  TaskRegistryEntry → WorkerRegistryEntry, TaskObserver →
  WorkerObserver, all Bus*TaskMessage → Bus*WorkerMessage,
  BusAddTaskMessage.task field → worker, BusWorkerRegistryMessage.tasks
  field → workers.
- Methods/decorators: activate_task → activate_worker, deactivate_task
  → deactivate_worker, add_task → add_worker, watch_task →
  watch_worker, @task_ready → @worker_ready, setup_pipeline_task hook
  → setup_pipeline_worker.
- Params/fields: FrameProcessorSetup.pipeline_task and
  FunctionCallParams.pipeline_task → pipeline_worker. Parameter names
  like task_name → worker_name; spawn/run accept worker:.
- Files: pipeline/base_task.py → base_worker.py, pipeline/task.py →
  worker.py (plus a re-export shim at pipeline/task.py),
  task_observer.py → worker_observer.py, task_ready_decorator.py →
  worker_ready_decorator.py, pipecat.tasks → pipecat.workers,
  llm_task.py → llm_worker.py, llm_context_task.py →
  llm_context_worker.py, examples/multi-task → examples/multi-worker.

Back-compat:
- PipelineTask kept as a deprecated subclass of PipelineWorker that
  warns on construction.
- pipecat.pipeline.task re-exports PipelineWorker/PipelineTask/etc. so
  existing user imports keep working.
- FrameProcessor.pipeline_task kept as a deprecated property that
  forwards to pipeline_worker.

Local variables in examples that hold a worker (task = PipelineTask(...))
are renamed to worker = PipelineWorker(...). Asyncio-task locals
(runner_task, etc.) are preserved.

tests/test_websocket_proxy.py

@@ -10,12 +10,12 @@ from unittest.mock import MagicMock
 
 from pipecat.bus import (
     AsyncQueueBus,
-    BusAddTaskMessage,
+    BusAddWorkerMessage,
     BusDataMessage,
 )
 from pipecat.bus.serializers import JSONMessageSerializer
-from pipecat.pipeline.base_task import BaseTask
-from pipecat.registry import TaskRegistry
+from pipecat.pipeline.base_worker import BaseWorker
+from pipecat.registry import WorkerRegistry
 from pipecat.utils.asyncio.task_manager import TaskManager, TaskManagerParams
 
 
@@ -85,17 +85,17 @@ class FakeStarletteWebSocket:
 class TestWebSocketProxyClientTask(unittest.IsolatedAsyncioTestCase):
     async def asyncSetUp(self):
         self.bus, self.tm = await create_test_bus()
-        self.registry = TaskRegistry(runner_name="test-runner")
+        self.registry = WorkerRegistry(runner_name="test-runner")
         self.serializer = JSONMessageSerializer()
 
     async def _create_client(self, fake_ws):
-        from pipecat.tasks.proxy.websocket.client import WebSocketProxyClientTask
+        from pipecat.workers.proxy.websocket.client import WebSocketProxyClientTask
 
         task = WebSocketProxyClientTask(
             "proxy",
             url="ws://fake",
-            remote_task_name="worker",
-            local_task_name="voice",
+            remote_worker_name="worker",
+            local_worker_name="voice",
             serializer=self.serializer,
         )
         task.attach(registry=self.registry, bus=self.bus)
@@ -141,9 +141,9 @@ class TestWebSocketProxyClientTask(unittest.IsolatedAsyncioTestCase):
         fake_ws = FakeWebSocket()
         task = await self._create_client(fake_ws)
 
-        stub = MagicMock(spec=BaseTask)
+        stub = MagicMock(spec=BaseWorker)
         stub.name = "child"
-        msg = BusAddTaskMessage(source="parent", target="worker", task=stub)
+        msg = BusAddWorkerMessage(source="parent", target="worker", worker=stub)
         await task.on_bus_message(msg)
 
         self.assertEqual(len(fake_ws._sent), 0)
@@ -208,17 +208,17 @@ class TestWebSocketProxyClientTask(unittest.IsolatedAsyncioTestCase):
 class TestWebSocketProxyServerTask(unittest.IsolatedAsyncioTestCase):
     async def asyncSetUp(self):
         self.bus, self.tm = await create_test_bus()
-        self.registry = TaskRegistry(runner_name="test-runner")
+        self.registry = WorkerRegistry(runner_name="test-runner")
         self.serializer = JSONMessageSerializer()
 
     async def _create_server(self, fake_ws):
-        from pipecat.tasks.proxy.websocket.server import WebSocketProxyServerTask
+        from pipecat.workers.proxy.websocket.server import WebSocketProxyServerTask
 
         task = WebSocketProxyServerTask(
             "gateway",
             websocket=fake_ws,
-            task_name="worker",
-            remote_task_name="voice",
+            worker_name="worker",
+            remote_worker_name="voice",
             serializer=self.serializer,
         )
         task.attach(registry=self.registry, bus=self.bus)