Don't deserialize utf8 data as native strings in Rust backend

[teh-cmc]

We currently do the obvious and slow thing: deserializing utf8arrays as native strings, which means a lot of copies, utf8 checks, etc.

We should instead keep raw Buffer<u8>s around and provide helpers to turn them into Cow<str> just in time, or something along these lines.

This of course extends to other types beyond strings; in fact it applies to any component with an inner type that is in and of itself plural: Binary, List<NativeT>, ...

[emilk]

• Very similar to Optimize text logs #1887

[emilk]

• This was implemented in Pass through strings using arrow2::Buffers #2931 and is now just awaiting Text migration to archetypes #2793