[Rust] Use `Vec<u8>` for hash key instead

[asfimport]

Is faster and decouples hash from aggregate implementation.

Reporter: Daniël Heres / @Dandandan
Assignee: Daniël Heres / @Dandandan

PRs and other links:

• GitHub Pull Request #8863

_{Note: This issue was originally created as ARROW-10837. Please see the migration documentation for further details.}

[asfimport]

Jorge Leitão / @jorgecarleitao:
Issue resolved by pull request 8863
#8863