truncate method
Implementation
Future<void> truncate() async {
if (_closed) return;
await _flush();
final rec = WalRecord(
op: WalOp.checkpoint,
table: '_global',
payload: {'lsn': _lsn, 'ts': DateTime.now().millisecondsSinceEpoch},
lsn: _lsn,
txnId: 0,
checksum: 0,
);
final line = '${rec.encode()}\n';
await _vfs.writeAll(path, Uint8List.fromList(utf8.encode(line)));
}