Messenger example - user search

• Add UserSearchFeature library to messenger example.
• Implement user search in messenger example.

Sources/XXClient/Functions/GetSingleUseParams.swift

@@ -19,7 +19,7 @@ extension GetSingleUseParams {
 }
 
 extension GetSingleUseParams {
-  public static let unimplemented = GetCMixParams(
+  public static let unimplemented = GetSingleUseParams(
     run: XCTUnimplemented("\(Self.self)", placeholder: "unimplemented".data(using: .utf8)!)
   )
 }