Migrate ArrowBuffer wrapper to expose arrow-rs buffers rather than arrow2

[jleibs]

#2970 introduced a new ArrowBuffer wrapper to return native arrow buffers on the deserialization path for Tensor types.

These buffers currently use arrow2::Buffer. In order to facilitate the future migration to arrow-rs, these can be made to wrap arrow-rs::Buffer instead. The types have convenient converters: https://docs.rs/arrow2/latest/arrow2/buffer/struct.Buffer.html#impl-From%3CBuffer%3CT%3E%3E-for-Buffer but we need to investigate whether these converters are still zero-copy.

One benefit of this migration is arrow-rs buffers use half:f16 whereas arrow2 buffers use arrow2::types::f16