refactor(pynumaflow-lite): Pythonic APIs for BatchMapper

[BulkBeing]

Similar to: #374

See: packages/pynumaflow-lite/manifests/batchmap/batchmap_cat.py
From a user's perspective, the code will look like:

class SimpleBatchCat(BatchMapper):
    async def handler(self, batch: AsyncIterable[Datum]) -> list[BatchResponse]:
        responses = []
        async for datum in batch:
            if datum.value == b"bad world":
                responses.append(BatchResponse(datum.id, Message.to_drop()))
            else:
                responses.append(BatchResponse(datum.id, Message(datum.value, keys=datum.keys)))
        return responses


async def main() -> None:
    print("Starting BatchMap server")
    # `serve` returns when SIGINT or SIGTERM arrives.
    await BatchMapAsyncServer(SimpleBatchCat()).serve()
    print("BatchMap server stopped")


if __name__ == "__main__":
    asyncio.run(main())

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.99%. Comparing base (5e64760) to head (88dc279).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #382   +/-   ##
=======================================
  Coverage   92.99%   92.99%           
=======================================
  Files          68       68           
  Lines        3656     3656           
  Branches      236      236           
=======================================
  Hits         3400     3400           
  Misses        190      190           
  Partials       66       66           

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[BulkBeing]

all names are already added in as a static list above