Omit type-checking on append

Currently on append "instanceof Uint8array" is called on every element, which does have an effect on the performance. It would be ideal instead that append method would only accept Uint8array and utilize Typescript types to make sure we are not appending things of wrong type.

For the case where we want to append UInt8ArrayList, we could have a separate method like, `join` or `merge` to cover that specific case.

For the append-all benchmark I can get 5.9m ops/s without type checking
and 5.5m ops/s with type checking