Deprecate passing a worker to PipelineRunner.run()

Register the worker with PipelineRunner.add_workers() before calling
run() instead. The worker argument still works but now emits a
DeprecationWarning and will be removed in a future release.

Update the runner docstrings, the run_test() helper, and all examples
(including the asyncio.gather() forms) to use the new pattern.

examples/getting-started/03a-local-still-frame.py

@@ -57,7 +57,8 @@ async def main():
                 tk_root.update_idletasks()
                 await asyncio.sleep(0.1)
 
-        await asyncio.gather(runner.run(worker), run_tk())
+        await runner.add_workers(worker)
+        await asyncio.gather(runner.run(), run_tk())
 
 
 if __name__ == "__main__":