[FEA] We have async_buffer(mr, count, uninit) but not buffer(mr, count, uninit)

[brycelelbach]

I believe you can spell an async uninitialized buffer with async_buffer(mr, count, uninit) instead of using uninitialized_async_buffer, but there's no corresponding synchronous buffer. This dichotomy is a bit annoying; we should be consistent here.

[miscco]

The issue at hand is that under the hood we would want any synchronous buffer to still be async. With that we opted to not go for it initially