pynumaflow-lite: Pythonic APIs for mapstreamer

[BulkBeing]

Similar to #382

Changed handler signature from handler(self, keys: list[str], datum: Datum) to handler(self, datum: Datum) as the keys are available in datum.keys. This is consistent with all map variants now.

Usage will look like:

class SimpleStreamCat(MapStreamer):
    async def handler(self, datum: Datum) -> AsyncIterator[Message]:
        if not datum.value:
            yield Message.to_drop()
            return
        for s in datum.value.decode("utf-8").split(","):
            yield Message(s.encode(), keys=datum.keys)


async def main() -> None:
    print("Starting MapStream server")
    # `serve` returns when SIGINT or SIGTERM arrives.
    await MapStreamAsyncServer(SimpleStreamCat()).serve()
    print("MapStream 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 (3403754) to head (c3d9a28).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #383   +/-   ##
=======================================
  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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