KeyLenOf
* Use correct length for Pallet and Storage prefix when calculating `KeyLenOf` * Add tests Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>