Canary system for most used dependents?

[ralphtheninja]

It would be nice to have some sort of canary system we can run to test effects in commonly used and important dependents based on abstract-leveldown.

This would help tremendously and avoid issues like #71

[ralphtheninja]

Note: This could be a generic system that doesn't have anything to do with abstract-leveldown.

[ralphtheninja]

@nolanlawson Mentioned https://github.com/bahmutov/dont-break over here #85 (comment) where we broke memdown again.

[vweevers]

May also want to canary test flumeview-level and encoding-down, see Level/encoding-down#42.