Alignment verification for both ConcreteBuffer and BufferExpander

[tigercosmos]

Ensure alignment verification for both ConcreteBuffer and BufferExpander. Upon casting the raw buffer to typed data, it is imperative to validate if the alignment meets the required alignment. This alignment validation should be implemented without utilizing a template and must be enforced within the buffer's allocator.

Original discussion from #304 (comment)

[tigercosmos]

@yungyuc I think for a while, I cannot think of a case in the memory that could be not in alignment. Currently, SimpleCollector holds a BufferExpander, and SimpleCollector never exchanges the expander with another SimpleCollector in another type.

For example, SimpleCollector<int> will not exchange the underlying expander with the one of SimpleCollector<double>.

In addition, a SimpleCollector will never expand the buffer with a different alignment of the buffer. Therefore, I wonder if this issue is still valid. Do you have any thoughts on this?

[yungyuc]

When implementing BufferExpander, I planned to align the memory at allocation. It calls an abstraction layer for multi-platform code. On mac the alignment allocation is unnecessary because malloc() is always aligned.

The alignment may be a thing for GPU. But I agree we do not need to do anything about it because we do not even have a GPU CI runner.

If you do not think alignment is a thing, we can close this issue for now. Let me do it.