Update asyncio_reduce example

[BulkBeing]

This example refers to a class that no longer exists

numaflow-python/packages/pynumaflow/examples/reduce/asyncio_reduce/executorpool.py

Line 139 in bcdc4c3

grpc_server = AsyncReducer(handler=handler.reduce_handler)

[IlyasFardaouix]

I think I see the issue here. The asyncio_reduce example is referencing the executorpool.py file which was removed in the bcdc4c3e5b557586f81ab0194fb335d937287e2f commit. This might be causing the example to break. I'd suggest updating the example to use the current implementation of the Accumulator class. Specifically, I'd like to know if you've considered updating the StreamSorter class to use the AccumulatorAsyncServer class instead of Accumulator, as the latter seems to be deprecated.