Additional test for uN::{gather,scatter}_bits Feature gate: #![feature(uint_gather_scatter_bits)] Tracking issue: https://github.com/rust-lang/rust/issues/149069 Accepted ACP: https://github.com/rust-lang/libs-team/issues/695#issuecomment-3549284861 Adds an additional runtime test for `uN::gather_bits` and `uN::scatter_bits` in coretests. They are each other's inverses in a sense, so a shared test can test both with relative ease. I plan to follow up with optimized implementations for these functions.