Improved: snapshot version pinning for call activities and global tasks

Overview When publishing a new version of a process model, the snapshot for the previous version now preserves links to the exact versions of: Call activities (process models), and Global tasks that were current at the time the snapshot was created. Call activities Call activities in a snapshot are now pinned to the specific process model version referenced at snapshot creation, not updated to newer versions. Global tasks Global tasks in a snapshot are now pinned to the specific global task version (including archived versions) that existed at snapshot creation. Snapshots Snapshots are only created when a new process model version is created/published, and all referenced call activities and global tasks are version-locked to that point in time.