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

首先定位 TypeScript 的 append 实现和 append-all benchmark。检查 append 当前如何处理 Uint8ArrayList，以及有哪些公共 API 或测试覆盖它。完成的标准是：明确规定所提议的 append 行为以及任何单独的 join 或 merge API，并由 benchmark 确认预期的性能变化。

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