fix: update GetPage to check for empty items slice

Refactor the GetPage function to check for an empty slice of items 
instead of a nil pointer. Update tests to cover cases for nil and 
empty slices, ensuring consistent behavior and improved clarity.

pagination.go

@@ -52,7 +52,7 @@ func EncodeCursor(cursor string) string {
 }
 
 func GetPage[T any](items []T, first *int, after *string, last *int, before *string, max int, fn func(T) string) ([]T, PageInfo) {
-	if items == nil {
+	if len(items) == 0 {
 		return nil, PageInfo{}
 	}
 	tmp := min(max, len(items))