arrow

ARROW-12687: [C++][Python][Dataset] Convert Scanner into a RecordBatchReader

This provides compatibility with APIs that expect regular RecordBatchReaders, e.g. exporting via the C Data Interface.

Closes #10268 from lidavidm/arrow-12687

Authored-by: David Li <li.davidm96@gmail.com>
Signed-off-by: David Li <li.davidm96@gmail.com>