Migrate from simulation/interaction/collaboration to activity/groupActivity

We will deprecate the entry points `simulationOf`, `interactionOf`, `collaborationOf`, and `unsafeCollaborationOf`, and replace them with new entry points `activityOf`, `groupActivityOf`, and `unsafeGroupActivityOf`.

The new entry points differ in that they do not take a separate time-step function as an argument. Instead, the time step function is included in `Event` as a new constructor called `TimePassing`.

Start by locating the simulationOf, interactionOf, collaborationOf, and unsafeCollaborationOf entry points, then find the Event definition and its proposed TimePassing constructor. Trace how the activityOf, groupActivityOf, and unsafeGroupActivityOf APIs are used. Done means the old entry points are migrated or deprecated and the new time-step behavior is integrated consistently.

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