make favorites work with reload/reconfigure

needed to implement a proper `==`, the default was comparing the full view model, which is not what we want

#1

Example/Sources/Grid/GridColorCellViewModel.swift

@@ -29,4 +29,10 @@ struct GridColorCellViewModel: CellViewModel {
         cell.label.text = self.color.name
         cell.backgroundColor = self.color.uiColor
     }
+
+    // MARK: Equatable
+
+    public static func == (left: GridColorCellViewModel, right: GridColorCellViewModel) -> Bool {
+        left.color == right.color
+    }
 }

Example/Sources/Grid/GridPersonCellViewModel.swift

@@ -35,4 +35,10 @@ struct GridPersonCellViewModel: CellViewModel {
         let personVC = PersonViewController(person: self.person)
         controller.navigationController?.pushViewController(personVC, animated: true)
     }
+
+    // MARK: Equatable
+
+    public static func == (left: GridPersonCellViewModel, right: GridPersonCellViewModel) -> Bool {
+        left.person == right.person
+    }
 }

Example/Sources/List/ListColorCellViewModel.swift

@@ -43,4 +43,10 @@ struct ListColorCellViewModel: CellViewModel {
             cell.accessories = []
         }
     }
+
+    // MARK: Equatable
+
+    public static func == (left: ListColorCellViewModel, right: ListColorCellViewModel) -> Bool {
+        left.color == right.color
+    }
 }

Example/Sources/List/ListPersonCellViewModel.swift

@@ -53,4 +53,10 @@ struct ListPersonCellViewModel: CellViewModel {
         let personVC = PersonViewController(person: self.person)
         controller.navigationController?.pushViewController(personVC, animated: true)
     }
+
+    // MARK: Equatable
+
+    public static func == (left: ListPersonCellViewModel, right: ListPersonCellViewModel) -> Bool {
+        left.person == right.person
+    }
 }

Sources/DiffableDataSource.swift

@@ -55,6 +55,9 @@ extension _DiffableDataSource {
                 destinationSnapshot.reloadItems(itemsToReload)
             }
 
+            // TODO: reload headers/footers and supplementary views?
+            // (gets out-of-sync when deleting items)
+
             self.applySnapshot(destinationSnapshot, animated: animated, completion: completion)
     }