This PR contains the work done to decouple the direct use of the `ModelContext` from `SwiftData` from the view model that uses it. In addition, the project transitioned to use Swift 6 and strict concurrency which brought some issues with the unit tests, so they were amended as well. Reviewed-on: rock-n-code/todos-app#8 Co-authored-by: Javier Cicchelli <javier@rock-n-code.com> Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>