1. This change extracts the logic responsible for updating dataLim from collections out of Axes.add_collection into a helper _update_collection_limits.
   Previously, add_collection contained the full autoscaling logic for collections. This made the method responsible for both adding the artist and computing its limits.
   By moving the limit computation into _update_collection_limits, add_collection now delegates that responsibility to a helper method, mirroring the pattern used for other artist types. This improves separation of responsibilities and prepares the codebase for the conditional autoscaling mechanism introduced in PR1.

2.Functionally, add_collection behaves the same as before for users. When autolim=True, the collection contributes its data limits to the axes and may trigger a view autoscale.
The difference is purely structural: the computation of collection limits is now delegated to _update_collection_limits, making add_collection primarily responsible for registering the artist with the axes.

3.This change does not alter the behavior of relim(). Collections still expose their data limits via get_datalim, and relim() continues to query artists in the same way as before.
The new helper simply centralizes the logic used when limits are updated during add_collection.

4. The autolim parameter was initially included so the helper could determine whether to trigger a view autoscale (_request_autoscale_view). However, after reconsidering consistency with the other _update_*_limits helpers, it may be cleaner for the helper to only update dataLim, leaving the decision about requesting autoscaling to the caller.
   I can adjust the implementation accordingly if that aligns better with the existing design.