Concurrent batch fetches

$github = Git::github();

$result = $github->batch()->languages(['acme/api', 'acme/web']); // BatchResult<array<string,int>>

$result->results();          // ['acme/api' => ['PHP' => 80, ...], ...]
$result->get('acme/api');    // one key's result, or null
$result->successful();       // true when no key failed
$result->failed();
count($result);              // successful keys

foreach ($result->errors() as $key => $error) {   // BatchError: key, status, message
    report("{$key} failed with {$error->status}");
}

$result->throwOnError();     // raises BatchRequestException if any key failed

$github->batch()->repositories(['acme/api', 'acme/web']);            // BatchResult<Repository>
$github->batch()->contents('acme/api', ['README.md', 'composer.json']); // BatchResult<FileContent>, keyed by file
$github->batch()->contents('acme/api', ['README.md'], ref: 'develop');
$github->batch()->pullRequest(['main' => 'acme/api#7']);             // id => PullRequest, ref "path#number"