feat(algorithms): add live metrics to algorithm pages

Each algorithm page shows its numbers with app-metrics.
FpsCounter publishes a rate every 500 ms, not every frame.
Fractal 2D reset now also resets the zoom slider.

src/app/shared/fps-counter.spec.ts

@@ -0,0 +1,30 @@
+import {FpsCounter} from './fps-counter';
+
+describe('FpsCounter', () => {
+  const FRAME_MS = 1000 / 60;
+
+  it('publishes 60 after the first 500 ms window and not before', () => {
+    const counter = new FpsCounter();
+    const at = (frame: number) => 1 + FRAME_MS * frame;
+
+    for (let frame = 0; at(frame) - 1 < 500; frame++) {
+      counter.tick(at(frame));
+    }
+    expect(counter.fps()).toBe(0);
+
+    counter.tick(at(30)); // 30 ticks since the window opened, 500 ms elapsed
+    expect(counter.fps()).toBe(60);
+  });
+
+  it('reset sets the rate back to 0', () => {
+    const counter = new FpsCounter();
+    for (let i = 0; i <= 61; i++) {
+      counter.tick(1 + FRAME_MS * i);
+    }
+    expect(counter.fps()).toBeGreaterThan(0);
+
+    counter.reset();
+
+    expect(counter.fps()).toBe(0);
+  });
+});