Add shorthand property for entity identifier in Derived

Sources/VergeNormalizationDerived/EntityType+Typealias.swift

@@ -1,7 +1,21 @@
-
 extension EntityType {
 
   public typealias Derived = Verge.Derived<EntityWrapper<Self>>
   public typealias NonNullDerived = Verge.Derived<NonNullEntityWrapper<Self>>
 
 }
+
+extension Derived where Value: NonNullEntityWrapperType {
+
+  public var entityID: Value.Entity.TypedID {
+    self.state.id
+  }
+}
+
+extension Derived where Value: EntityWrapperType {
+
+  public var entityID: Value.Entity.TypedID? {
+    self.state.id
+  }
+
+}

Sources/VergeNormalizationDerived/EntityWrapper.swift

@@ -1,9 +1,16 @@
 import Normalization
 
+public protocol EntityWrapperType {
+  associatedtype Entity: EntityType
+
+  var id: Entity.TypedID { get }
+}
+
 /// A value that wraps an entity and results of fetching.
-public struct EntityWrapper<Entity: EntityType>: Sendable {
+public struct EntityWrapper<Entity: EntityType>: Sendable, EntityWrapperType {
 
-  public private(set) var wrapped: Entity?
+  public let wrapped: Entity?
+
   public let id: Entity.TypedID
 
   public init(id: Entity.TypedID, entity: Entity?) {

Sources/VergeNormalizationDerived/NonNullEntityWrapper.swift

@@ -1,11 +1,17 @@
 import Normalization
 
+public protocol NonNullEntityWrapperType {
+  associatedtype Entity: EntityType  
+
+  var id: Entity.TypedID { get }
+}
+
 /// A value that wraps an entity and results of fetching.
 @dynamicMemberLookup
-public struct NonNullEntityWrapper<Entity: EntityType> {
+public struct NonNullEntityWrapper<Entity: EntityType>: Sendable, NonNullEntityWrapperType {
 
   /// An entity value
-  public private(set) var wrapped: Entity
+  public let wrapped: Entity
 
   /// An identifier
   public let id: Entity.TypedID