Conversation open speed benchmarking for staging builds

Co-authored-by: Fedor Indutnyy <indutny@signal.org>

ts/util/benchmark/stats.ts

@@ -0,0 +1,40 @@
+// Copyright 2023 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+export type StatsType = {
+  mean: number;
+  stddev: number;
+  [key: string]: number;
+};
+
+export function stats(
+  list: ReadonlyArray<number>,
+  percentiles: ReadonlyArray<number> = []
+): StatsType {
+  if (list.length === 0) {
+    throw new Error('Empty list given to stats');
+  }
+
+  let mean = 0;
+  let stddev = 0;
+
+  for (const value of list) {
+    mean += value;
+    stddev += value ** 2;
+  }
+  mean /= list.length;
+  stddev /= list.length;
+
+  stddev -= mean ** 2;
+  stddev = Math.sqrt(stddev);
+
+  const sorted = list.slice().sort((a, b) => a - b);
+
+  const result: StatsType = { mean, stddev };
+
+  for (const p of percentiles) {
+    result[`p${p}`] = sorted[Math.floor((sorted.length * p) / 100)];
+  }
+
+  return result;
+}