Prevent collector snapshot rerender stalls

Memoize the collector content across unrelated app snapshots and release collapsed child rows from the DOM after their closing animation. Draw the idle speed sparkline as a pixel-aligned one-physical-pixel stroke so its thickness remains uniform across display scales.

tests/statistics-view.test.tsx

@@ -3,7 +3,7 @@ import { isValidElement, type ReactElement, type ReactNode } from "react";
 import { renderToStaticMarkup } from "react-dom/server";
 import { describe, expect, it } from "vitest";
 import type { DownloadItem, DownloadStatus, UiSnapshot } from "../src/shared/types";
-import { appendBandwidthSample, readBandwidthChartPalette, readDownloadSpeedSparklinePalette } from "../src/renderer/App";
+import { appendBandwidthSample, getIdleSparklineStroke, readBandwidthChartPalette, readDownloadSpeedSparklinePalette } from "../src/renderer/App";
 import {
   buildStatisticsViewModel,
   type StatisticsMetric
@@ -593,6 +593,12 @@ describe("bandwidth chart palette", () => {
     expect(palette).toEqual({ accent: "rgb(74, 222, 128)" });
   });
 
+  it("aligns the idle speed line to one physical pixel at every display scale", () => {
+    expect(getIdleSparklineStroke(22, 1)).toEqual({ y: 20.5, lineWidth: 1 });
+    expect(getIdleSparklineStroke(22, 1.25)).toEqual({ y: 20.4, lineWidth: 0.8 });
+    expect(getIdleSparklineStroke(22, 2)).toEqual({ y: 20.25, lineWidth: 0.5 });
+  });
+
   it("labels the live chart and slows redraws when reduced motion is requested", () => {
     const source = readFileSync(new URL("../src/renderer/App.tsx", import.meta.url), "utf8");
     const chartBlock = source.slice(source.indexOf("const BandwidthChart"), source.indexOf("interface DownloadSpeedSparklineProps"));