Review sessions: ability to start over while keeping the current "reviewed" status

I would love to be able to start a review again from scratch.
This would help improve the translations and making sure you didn’t miss something the first time around.

This requires handling more than one review session at a time.
Imagine you have 1000 keys and start over, then 5 keys are changed as you only re-reviewed 100 keys. You don’t want to be blocked because you have to review the 900 remaining keys. You should be able to validate the 5 key changes in your “main” review session and keep reviewing the rest in your other session at your own pace.