design change to persist all Event within EventGroup, including unsubscribed

[joeyoravec]

As discussed at the April 2024 vsomeip meeting, the current vsomeip design discards all unsubscribed Events within an EventGroup. Let's imagine that you're modeling:

• an as-built configuration DID like 0xDE00 where the value is fixed at vehicle assembly, and never changes at runtime
• having many subfields (aka. decoded bitfields) each represented as a separate Franca attribute
• where it would make sense to logically group these into a single EventGroup for efficiency

This diagram highlights the problem:

The only way I've identified to workaround this design limitation is with a 1:1 relationship; put each attribute into a unique EventGroup. It is very costly in terms of performance to have ~3500 total EventGroup and led to:

• [BUG]: vsomeip slow to establish communication with lots of EventGroup #669 needing to aggregate Service Discovery with the train logic
• [BUG]: vsomeip slow to restart with lots of EventGroup #690 needing to inhibit excessive restart() when SubscribeNack is received
• ...and probably a lot more

Starting this to discuss the best approach for this problem. It looks "pretty hard" within the existing object model to get these values persisted without a subscription.