[rust] Stream adapter for the bounded readers

[fresh-borzoni]

Search before asking

• I searched in the issues and found nothing similar.

Description

The bounded readers (RecordBatchLogReader, LimitBatchScanner) only expose next_batch().
Async consumers like DataFusion want a Stream.

An additive into_stream(self) -> impl Stream<Item = Result> on both, wrapping next_batch().

Willingness to contribute

• I'm willing to submit a PR!