Reconsider usages of AsyncRead and AsyncWrite in puffin

[evenyag]

As mentioned in #4037 (comment)

We still have more work to do moving forward. For example, we need to reconsider the use of AsyncRead + AsyncSeek in our codebase, as they are not suitable for object storage services and upcoming completion-based IO.

AsyncRead and AsyncWrite are not suitable for object stores. We might need to revisit the implementation of our puffin crate.

This is not an urgent problem that we must solve now.

[killme2008]

@zhongzc I think we should improve it before 1.0.