Followup code cleanup/optmization after #36319

[andy31415]

Once we have a single codepath, some optimizations become clearer:

• Enforce DataModel::Provider everywhere #36319 (comment) : IsDeviceTypeOnEndpoint logic is repeated in several places. Some code re-use would be nice.
• Enforce DataModel::Provider everywhere #36319 (comment) : reporting/Read.cpp is not ideally named, should be maybe inline into reporting or we should figure out proper naming and placement
• Enforce DataModel::Provider everywhere #36319 (comment) : mLastSuccessfullyWrittenPath and mProcessingAttributePath are tightly coupled so we may be able to save some code/logic/flash/ram. Review their use and coupling and update the code accordingly

[andy31415]

For the 3rd item, I could not find an immediate dedup logic for mLastSuccessfullyWrittenPath and mProcessingAttributePath as their code paths are updated at separate times. Deduplicating members within our handlers will likely require separate consideration.