add notion of Contracts in the metamodel and the textual editor
add abstract class Guard as parent for Contract and GuardedAction
Closes #150 (closed)
GitLab upgrade completed. Current version is 18.5.4
https://about.gitlab.com/releases/2025/09/18/gitlab-18-4-released/
https://about.gitlab.com/releases/2025/10/16/gitlab-18-5-released/
add abstract class Guard as parent for Contract and GuardedAction
Closes #150 (closed)