Ensure alignment for vortex-buffer

[robert3005]

Right now when creating Bytes based buffers we lose the alignment information. There has been no movement on issue to allow this tokio-rs/bytes#437 which would mean that unless allocator_api is stable this is unlikely to happen.

[gatesn]

I came across an aligned-buffer and aligned-buffer-pool as part of the Rkyv utilities repo: https://crates.io/crates/aligned-buffer

I will try to rebuild vortex-buffer (along with mutable and P-typed versions) around this crate and then we can move away from Arrow buffers, Bytes buffers, Vec<u8> and Vec<PType::NATIVE>.

[gatesn]

There is an open question though around how we handle unaligned buffers coming in from external systems.

[gatesn]

Dupe of #115