Misc notes on improvements and learnings from ReactiveCollectionsKit

At the time of this writing, there are various improvements in-progress. There has not been much activity here for awhile.

The goal of the next big release is to use diffable data sources, etc. See `FetchedResultsDiffableDataSource` in-progress.

In the meantime, [`ReactiveCollectionsKit `](https://github.com/jessesquires/ReactiveCollectionsKit) has advanced a lot. There are a lot of learnings there to bring in here regarding diffing.

### Notes

Random notes and links. Some of these are old and I don't remember the full context. Anyway, I'm putting them all here for when I finally come back to this project.

- `static var countResultType: NSFetchRequestResultType`
- [Changing The Core Data Test Store Location](https://useyourloaf.com/blog/changing-the-core-data-test-store-location/)
- [Debugging Core Data](https://useyourloaf.com/blog/debugging-core-data/)
- [Preventing unwanted fetches when using NSFetchedResultsController and fetchBatchSize](https://www.donnywals.com/preventing-unwanted-fetches-when-using-nsfetchedresultscontroller-and-fetchbatchsize/)
- [How-to use Diffable Data Sources with Core Data](https://www.avanderlee.com/swift/diffable-data-sources-core-data/)
- [How to create a Core Data fetch request using @FetchRequest](https://www.hackingwithswift.com/quick-start/swiftui/how-to-create-a-core-data-fetch-request-using-fetchrequest)