Stage 7b: the benchmark of the author keys and the sealing

tool/authorkey_bench.dart times on the VM and compiled to JavaScript the
generation of an author key, its Ed25519 signature of 99 bytes and of
1 MiB, the strict verification for comparison, its file encrypted with
scrypt of logN 16 and read again, sealLocator for round 1000 and
newEnvelope of a .dkc of 1 MiB.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tool/authorkey_bench.dart

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+// Times stage 7b of datekeys-dart on the VM and compiled to JavaScript: an
+// author key, generated, its Ed25519 signature of AUTHOR_MESSAGE (99 bytes)
+// and of 1 MiB, its file encrypted with scrypt of logN 16 and read again;
+// and the sealing of a locator of round 1000 and the envelope of a .dkc of
+// 1 MiB. Each is the median of a few runs. The random values come from the
+// CSPRNG of the platform, as in production.
+//
+//   dart run tool/authorkey_bench.dart
+//
+//   dart compile js -O2 -o authorkey_bench.js tool/authorkey_bench.dart
+//   node -e "globalThis.self = globalThis; require('./authorkey_bench.js')"
+//
+// ignore_for_file: avoid_print
+import 'dart:typed_data';
+
+import 'package:datekeys/datekeys.dart' show quicknet;
+import 'package:datekeys/src/authorkey.dart';
+import 'package:datekeys/src/curve25519.dart' show verifyStrict;
+import 'package:datekeys/src/locator.dart';
+import 'package:datekeys/src/locator_seal.dart';
+
+const isWeb = identical(0, 0.0);
+
+double median(List<double> xs) => (xs..sort())[xs.length ~/ 2];
+
+/// The median time of [f], in milliseconds, over [runs] runs.
+double time(int runs, void Function() f) {
+  final times = <double>[];
+  for (var i = 0; i < runs; i++) {
+    final sw = Stopwatch()..start();
+    f();
+    times.add(sw.elapsedMicroseconds / 1000);
+  }
+  return median(times);
+}
+
+String ms(double t) => t < 10 ? t.toStringAsFixed(2) : t.toStringAsFixed(0);
+
+void main() {
+  print('stage 7b, ${isWeb ? 'Node.js' : 'VM'}');
+  final key = AuthorKey.generate();
+  final msg = Uint8List(99);
+  final big = Uint8List(1 << 20);
+  // Warm up.
+  for (var i = 0; i < 20; i++) {
+    key.sign(msg);
+  }
+  print('AuthorKey.generate: ${ms(time(15, AuthorKey.generate))} ms');
+  print('Ed25519 sign, 99 bytes: ${ms(time(31, () => key.sign(msg)))} ms');
+  final sig = key.sign(msg);
+  print(
+    'Ed25519 verifyStrict, 99 bytes: '
+    '${ms(time(31, () => verifyStrict(key.publicKey, msg, sig)))} ms',
+  );
+  print('Ed25519 sign, 1 MiB: ${ms(time(7, () => key.sign(big)))} ms');
+  late Uint8List file;
+  print(
+    'encryptAuthorKey, scrypt logN 16: '
+    '${ms(time(5, () => file = encryptAuthorKey(key, 'a passphrase')))} ms',
+  );
+  print(
+    'readAuthorKey, scrypt logN 16: '
+    '${ms(time(5, () => readAuthorKey(file, passphrase: 'a passphrase')))} ms',
+  );
+  final e = newEnvelope(Uint8List(100));
+  final loc = e.locator.withAddresses([
+    LocatorAddress('https://example.com/rest'),
+  ]);
+  print(
+    'sealLocator, round 1000: '
+    '${ms(time(5, () => sealLocator(quicknet(), 1000, loc)))} ms',
+  );
+  print(
+    'newEnvelope, a .dkc of 1 MiB: '
+    '${ms(time(5, () => newEnvelope(big)))} ms',
+  );
+}