Function to activate mode using a list of methods

[fohrloop]

Splitting this work from #69 into its own ticket.

Task

• Create an activate() function which looks something like this

def activate(methods: list[MethodCls], ...) -> tuple[ActivationResult, HeartBeat|None]:
    prioritized_methods = prioritize_methods(methods)
    result = ActivationResult()

    for method in prioritized_methods:
        methodresult, heartbeat = activate_using(method, ...)
        result.add(methodresult)
        if result.success:
            break
    return result, heartbeat

• In this first version, the returned heartbeat can always be None and there will be separate task for creating the Heartbeat class. The Heartbeat might not be part of 0.8.0 release as there are no heartbeat-based Methods yet.

Related PRs:

• Issue 108: Introduce CallProcessor and ModeController #113
• Issue 108: Finalize activate() function #116