View more discover results (#1198)

## Description
Adds a card at the end of the rows on the discover page/tab to view more
results. When clicking this card, it goes to a grid view of more results
starting focused on the next one.

### Dev notes

This PR modifies `ApiRequestPager` to move most of its functionality
into an abstract class, `RequestPager`. And then add a new concrete
class, `DiscoverRequestPager`, for Seerr API paging. `ApiRequestPager`
remains for Jellyfin paging.

### Related issues
Related to #1035

### Testing
Emulator

## Screenshots

![discover_view_more
Large](https://github.com/user-attachments/assets/180aa7a5-45c3-4544-b3f8-e3d394859178)
![discover_grid
Large](https://github.com/user-attachments/assets/ae5e8fbf-0fa4-4a2e-96ac-629ae688c05d)

## AI or LLM usage
None

app/src/main/java/com/github/damontecres/wholphin/services/SeerrService.kt

@@ -191,6 +191,18 @@ class SeerrService
             return "${base}${prefix}$path"
         }
 
+        suspend fun createDiscoverItem(item: Any): DiscoverItem =
+            when (item) {
+                is MovieResult -> createDiscoverItem(item)
+                is MovieDetails -> createDiscoverItem(item)
+                is TvResult -> createDiscoverItem(item)
+                is TvDetails -> createDiscoverItem(item)
+                is SeerrSearchResult -> createDiscoverItem(item)
+                is CreditCast -> createDiscoverItem(item)
+                is CreditCrew -> createDiscoverItem(item)
+                else -> throw IllegalArgumentException("Unsupported type ${item::class.qualifiedName}")
+            }
+
         suspend fun createDiscoverItem(movie: MovieResult): DiscoverItem =
             DiscoverItem(
                 id = movie.id,