Support additional collection classes

We already support `NSArray` and `NSDictionary`. Additional candidates would be:

* [ ] [`NSFastEnumeration`](https://developer.apple.com/documentation/foundation/nsfastenumeration?language=objc), for generic iteration support over any Objective-C collection
* [ ] [`NSSet`](https://developer.apple.com/documentation/foundation/nsset?language=objc)
* [ ] [`NSCountedSet`](https://developer.apple.com/documentation/foundation/nscountedset?language=objc)
* [ ] Less common, more specialized collection classes? Not sure if these are all that useful.
* [ ] [`NSIndexSet`](https://developer.apple.com/documentation/foundation/nsindexset?language=objc)
* [ ] [`NSOrderedSet`](https://developer.apple.com/documentation/foundation/nsorderedset?language=objc)
* [ ] [`NSPointerArray`](https://developer.apple.com/documentation/foundation/nspointerarray?language=objc)
* [ ] [`NSMapTable`](https://developer.apple.com/documentation/foundation/nsmaptable?language=objc)
* [ ] [`NSHashTable`](https://developer.apple.com/documentation/foundation/nshashtable?language=objc)

Start by reviewing the existing NSArray and NSDictionary support in rubicon-objc and compare how the listed Objective-C collection classes would fit the bridge. Decide which candidates are in scope, then verify that the selected classes are supported consistently and that their behavior is covered by the project’s existing checks.

Written by the indexing model from the issue text.