Add Swift 6 support. Refine historyTokenStorage implementation.

[JPToroDev]

[JPToroDev]

Hi @yonat, just wanted to check in and see if you have any questions or concerns about my pull request.

[yonat]

Sorry, I have been too busy... will take a look on Friday.

[JPToroDev]

Sounds good—thank you!

[JPToroDev]

Hey @yonat. Just wanted to circle back here and see if there's any update on the pull request.

[JPToroDev]

Just pushed a new commit with your requested revisions. Let me know if you need anything else after you run and test!

[yonat]

Cool! Would you allow me to make changes to this PR? I have some stylistic modifications and I think it would be easier if I just do them.

[JPToroDev]

Excited to see them—go for it!

[yonat]

Thanks, please review the last 3 commits and see if it's okay by you.

[JPToroDev]

Very nice—especially the simplification of HistoryTokenStorage. One question: why go with classes over structs for its concrete implementations? Wouldn't structs be more lightweight?

[yonat]

If it's a struct then historyTokenStorage has to be a var and not a let, which results in warning:

Stored property 'historyTokenStorage' of 'Sendable'-conforming class 'ContactsChangeNotifier' is mutable; this is an error in the Swift 6 language mode

[JPToroDev]

Ah I see, don't know why that error didn't come up on my end. Everything looks great—thanks again for the improvements.