- Tweak the Update and Remove methods to reduce the number of dictionary lookups required.
- Change the Update method to an indexer, this allows simplifying callers who wanted to AddOrUpdate a value.
- Implement IDictionary<T, Rectangle>, since the class already implements these semantics by providing a backing store of the bounds for each item.
- Clean up some naming to use the generic `item` instead of `actor`.
- Make the MutateBins action methods static.