open static method
Implementation
static Future<Pager> open(String path, {required VfsAdapter vfs}) async {
final pager = Pager._(path, vfs);
pager._file = await vfs.openRaf(path);
// Compute existing page count from file size.
final size = await pager._file.length();
pager._totalPages = size ~/ pageSize;
return pager;
}