add missing src/waiting-guard.mjs from template

src/waiting-guard.mjs

@@ -0,0 +1,31 @@
+import { Guard } from "./guard.mjs";
+
+/**
+ * Shows a component during transition.
+ * @param {SvelteComponent} component to show up during th transition
+ * @param {number} rampUpTime initial delay for the componnt to show up
+ */
+export class WaitingGuard extends Guard {
+
+  #component;
+  #rampUpTime;
+
+  constructor(component, rampUpTime = 300) {
+    super();
+    this.#component = component;
+    this.#rampUpTime = rampUpTime;
+  }
+
+  async enter(transition) {
+    transition.timeoutID = setTimeout(() => {
+      transition.timeoutID = undefined;
+      transition.component = this.#component;
+    }, this.#rampUpTime);
+  }
+
+  async leave(transition) {
+    if (transition.timeoutID) {
+      clearTimeout(transition.timeoutID);
+    }
+  }
+}