Add MessengerDestroy functor

Sources/XXMessengerClient/Messenger/Functors/MessengerDestroy.swift

+import XCTestDynamicOverlay
+
+public struct MessengerDestroy {
+  public var run: () throws -> Void
+
+  public func callAsFunction() throws -> Void {
+    try run()
+  }
+}
+
+extension MessengerDestroy {
+  public static func live(_ env: MessengerEnvironment) -> MessengerDestroy {
+    MessengerDestroy {
+      try env.fileManager.removeDirectory(env.storageDir)
+      env.ud.set(nil)
+      env.e2e.set(nil)
+      env.cMix.set(nil)
+    }
+  }
+}
+
+extension MessengerDestroy {
+  public static let unimplemented = MessengerDestroy(
+    run: XCTUnimplemented("\(Self.self)")
+  )
+}