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_job_group.py

@@ -13,7 +13,7 @@ from pipecat.bus import (
     BusJobRequestMessage,
     BusJobResponseMessage,
 )
-from pipecat.pipeline.base_task import BaseTask
+from pipecat.pipeline.base_worker import BaseWorker
 from pipecat.pipeline.job_context import (
     JobError,
     JobEvent,
@@ -21,16 +21,16 @@ from pipecat.pipeline.job_context import (
     JobGroupEvent,
     JobStatus,
 )
-from pipecat.registry import TaskRegistry
-from pipecat.registry.types import TaskReadyData
+from pipecat.registry import WorkerRegistry
+from pipecat.registry.types import WorkerReadyData
 from pipecat.utils.asyncio.task_manager import TaskManager, TaskManagerParams
 
 
-class StubTask(BaseTask):
+class StubTask(BaseWorker):
     pass
 
 
-class JobWorkerTask(BaseTask):
+class JobWorkerTask(BaseWorker):
     """Worker that automatically responds to job requests via the bus."""
 
     def __init__(self, name, *, response=None, status=JobStatus.COMPLETED):
@@ -43,7 +43,7 @@ class JobWorkerTask(BaseTask):
         await self.send_job_response(message.job_id, self._auto_response, status=self._auto_status)
 
 
-class UrgentJobWorkerTask(BaseTask):
+class UrgentJobWorkerTask(BaseWorker):
     """Worker that responds urgently to job requests."""
 
     def __init__(self, name, *, response=None, status=JobStatus.COMPLETED):
@@ -58,7 +58,7 @@ class UrgentJobWorkerTask(BaseTask):
         )
 
 
-class UpdatingWorkerTask(BaseTask):
+class UpdatingWorkerTask(BaseWorker):
     """Worker that sends updates before responding."""
 
     def __init__(self, name, *, updates, response=None):
@@ -73,7 +73,7 @@ class UpdatingWorkerTask(BaseTask):
         await self.send_job_response(message.job_id, self._auto_response)
 
 
-class StreamingWorkerTask(BaseTask):
+class StreamingWorkerTask(BaseWorker):
     """Worker that streams data before responding."""
 
     def __init__(self, name, *, chunks, response=None):
@@ -89,7 +89,7 @@ class StreamingWorkerTask(BaseTask):
         await self.send_job_stream_end(message.job_id, self._auto_response)
 
 
-class SlowWorkerTask(BaseTask):
+class SlowWorkerTask(BaseWorker):
     """Worker that blocks during job execution until cancelled."""
 
     def __init__(self, name):
@@ -113,7 +113,7 @@ async def create_test_env():
     tm.setup(TaskManagerParams(loop=asyncio.get_running_loop()))
     await bus.setup(tm)
     await bus.start()
-    registry = TaskRegistry(runner_name="test-runner")
+    registry = WorkerRegistry(runner_name="test-runner")
     return bus, tm, registry
 
 
@@ -122,7 +122,7 @@ async def setup_task(bus, registry, task):
     task.attach(registry=registry, bus=bus)
     await task.setup(bus.task_manager)
     await bus.subscribe(task)
-    await registry.register(TaskReadyData(task_name=task.name, runner="test-runner"))
+    await registry.register(WorkerReadyData(worker_name=task.name, runner="test-runner"))
 
 
 def capture_bus(bus):
@@ -351,7 +351,7 @@ class TestJobGroupContext(unittest.IsolatedAsyncioTestCase):
 
         self.assertEqual(len(events), 2)
         self.assertEqual(events[0].type, JobGroupEvent.UPDATE)
-        self.assertEqual(events[0].task_name, "worker")
+        self.assertEqual(events[0].worker_name, "worker")
         self.assertEqual(events[0].data, {"progress": 25})
         self.assertEqual(events[1].data, {"progress": 75})
         self.assertEqual(tg.responses, {"worker": {"result": "done"}})
@@ -405,7 +405,7 @@ class TestJobGroupContext(unittest.IsolatedAsyncioTestCase):
 
         self.assertEqual(len(events), 1)
         self.assertEqual(events[0].type, JobGroupEvent.UPDATE)
-        self.assertEqual(events[0].task_name, "w1")
+        self.assertEqual(events[0].worker_name, "w1")
         self.assertEqual(tg.responses, {"w1": {"a": 1}, "w2": {"b": 2}})
 
     async def test_job_group_no_iteration_still_works(self):