Callback on keychain value change for given key

[LeonidKokhnovich]

Hi! Thanks a lot for such a great library!

I would like to see if there could be an integration with Swift Combine which would allow getting updates to the Keychain reactively as a stream of changes when they happen. What is the feasibility of that?

Any other way to expose callback when a change happens like KVO, Notification or delegate would also be a great start.