refactor scan to avoid blocking (#307)

currently scan match pattern count 100 will not return until finding 100 matched pattern values. This will block the processing. Refactor scan logic to make it consistent with Redis. 

Co-authored-by: lokax <m632656684@gmail.com>

fix readonly error not reported

New tag 0.8.22

New tag 0.8.21

chore: fix tag issue.

update