Improve compatibility with strict concurrency

Fixes #167

Author: sindresorhus

Sources/Defaults/Defaults.swift

@@ -43,7 +43,7 @@ extension Defaults {
 	/**
 	Type-erased key.
 	*/
-	public class _AnyKey {
+	public class _AnyKey: @unchecked Sendable {
 		public typealias Key = Defaults.Key
 
 		public let name: String

Sources/Defaults/Observation.swift

@@ -27,7 +27,7 @@ public protocol _DefaultsObservation: AnyObject {
 extension Defaults {
 	public typealias Observation = _DefaultsObservation
 
-	public enum ObservationOption {
+	public enum ObservationOption: Sendable {
 		/**
 		Whether a notification should be sent to the observer immediately, before the observer registration method even returns.
 		*/
@@ -365,3 +365,4 @@ extension Defaults.ObservationOptions {
 }
 
 extension Defaults.KeyChange: Equatable where Value: Equatable {}
+extension Defaults.KeyChange: Sendable where Value: Sendable {}