feat: enhance timer

kernel/include/util/function.h

@@ -23,3 +23,10 @@ auto construct() {
         return Type{forward<decltype(args)>(args)...};
     };
 }
+
+template<typename V>
+auto constant(V v) {
+    return [v](auto _) {
+        return v;
+    };
+}

kernel/include/util/optional.h

@@ -183,3 +183,24 @@ public:
         }
     }
 };
+
+template<typename T>
+struct as_optional {
+    using type = optional<T>;
+};
+template<typename T>
+struct as_optional<optional<T>> {
+    using type = optional<T>;
+};
+template<typename T>
+using as_optional_t = typename as_optional<T>::type;
+
+template<typename Func>
+auto lift(Func func) {
+    return [func](const auto&... optionals) -> as_optional_t<decltype(func(optionals.value()...))> {
+        if ((optionals.has_value() && ...)) {
+            return func(optionals.value()...);
+        }
+        return nullopt;
+    };
+}