[Rust] Remove UB on parquet crate #26742

While trying to remove the unsafe FatPtr, I stumbled upon the borrow checker not allowing the code to compile, which suggests that the FatPtr is being used to bypass the borrow checked, which I do not think is intentional.

Reporter: Jorge Leitão / @jorgecarleitao
Assignee: Jorge Leitão / @jorgecarleitao

PRs and other links:

• GitHub Pull Request #8829

_{Note: This issue was originally created as ARROW-10804. Please see the migration documentation for further details.}