[rust] Stream adapter for bounded readers (DataFusion interop)

[fresh-borzoni]

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• I searched in the issues and found nothing similar.

Description

Give LimitBatchScanner and RecordBatchLogReader an into_stream() returning a Stream<Item = Result>, plus a bare-RecordBatch bridge for DataFusion/PyArrow (like the existing SyncRecordBatchLogReader). Additive - keep next_batch(). Do both readers together so the client gets one consistent stream surface.

Willingness to contribute

• I'm willing to submit a PR!