Store and retrieve Codable objects to various persistence layers

struct User: Codable {
	var id: Int
	var firstName: String
	var lastName: String
	var laptop: Laptop?
}

struct Laptop: Codable {
	var model: String
	var name: String
}

struct User: Codable, Identifiable {
	static let idKey = \User.id
	...
}

struct Laptop: Codable, Identifiable {
	static let idKey = \Laptop.model
	...
}

// To save objects to UserDefaults, create UserDefaultsStore:
let usersStore = UserDefaultsStore<User>(uniqueIdentifier: "users")!
let laptopsStore = UserDefaultsStore<Laptop>(uniqueIdentifier: "laptops")!

// To save a single object to UserDefaults, create UserDefaultsStore:
let userStore = SingleUserDefaultsStore<User>(uniqueIdentifier: "user")!

// To save objects to the file system, create FilesStore:
let usersStore = FilesStore<User>(uniqueIdentifier: "users")
let laptopsStore = FilesStore<Laptop>(uniqueIdentifier: "laptops")

// To save a single object to the file system, create SingleFilesStore:
let userStore = SingleFilesStore<User>(uniqueIdentifier: "user")

// To save a single object to the system's keychain, create SingleKeychainStore:
let userStore = SingleKeychainStore<User>(uniqueIdentifier: "user")

let macbook = Laptop(model: "A1278", name: "MacBook Pro")
let john = User(userId: 1, firstName: "John", lastName: "Appleseed", laptop: macbook)

// Save an object to a store
try! usersStore.save(john)

// Save an array of objects to a store
try! usersStore.save([jane, steve, jessica])

// Get an object from store
let user = store.object(withId: 1)
let laptop = store.object(withId: "A1278")

// Get all objects in a store
let laptops = laptopsStore.allObjects()

// Check if store has an object
print(usersStore.hasObject(withId: 10)) // false

// Iterate over all objects in a store
laptopsStore.forEach { laptop in
	print(laptop.name)
}

// Delete an object from a store
usersStore.delete(withId: 1)

// Delete all objects in a store
laptops.deleteAll()

// Know how many objects are stored in a store
let usersCount = usersStore.objectsCount