Fast S3 verify and snapshot commit; shorter runs list; durations with days

On S3, index files and the tree segments read back when a snapshot is
written are fetched 16 at a time through the storage's S3 client
(IBackend::getRanges(), getMany()). Blobs that follow each other in a pack
are read as one range on every location. The snapshot is written in a step
of its own and the run shows "commit" meanwhile. On a 1 TB production
repository the check went from about 4 hours to 3.5 minutes.

backup:status and the web interface list the runs of the last 7 days,
running ones and at least the newest 5; --all / "Show older runs" list
all. Durations of a day or more show the days.

lib/Format.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+// SPDX-FileCopyrightText: 2026 Dillard Blom
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+namespace OCA\NgBackup;
+
+final class Format {
+	/** "12:10:13", or "1d 12:10:13" from a day on (a long first backup takes days). */
+	public static function duration(int $seconds): string {
+		$seconds = max(0, $seconds);
+		$days = intdiv($seconds, 86400);
+		$time = gmdate('H:i:s', $seconds % 86400);
+		return $days > 0 ? $days . 'd ' . $time : $time;
+	}
+}