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/Backend/GetsOneByOne.php

@@ -7,7 +7,7 @@ declare(strict_types=1);
 
 namespace OCA\NgBackup\Backend;
 
-/** IBackend::getMany() for a backend where reading files one after the other costs nothing extra. */
+/** IBackend::getMany() and getRanges() for a backend where reading one after the other costs nothing extra. */
 trait GetsOneByOne {
 	/**
 	 * @param list<string> $paths
@@ -27,4 +27,14 @@ trait GetsOneByOne {
 			yield $path => $data;
 		}
 	}
+
+	/**
+	 * @param list<array{0:string, 1:int, 2:int}> $ranges
+	 * @return \Generator<int, string>
+	 */
+	public function getRanges(array $ranges): \Generator {
+		foreach ($ranges as $i => [$path, $offset, $length]) {
+			yield $i => $this->getRange($path, $offset, $length);
+		}
+	}
 }