[python] Add asyncio-native streaming API for bounded log reading

[charlesdong1991]

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Description

LogScanner.to_arrow_batch_reader() currently returns a synchronous pyarrow.RecordBatchReader that blocks the calling thread on each __next__() call. This might be acceptable for Arrow interop (e.g., feeding into DuckDB, Polars etc), but is not suitable for asyncio-native Python code.

So, ideally we should add an async counterpart, e.g., async for batch in scanner.read_batches() which yields RecordBatch objects without blocking the event loop.

Willingness to contribute

• I'm willing to submit a PR!