Fix warnings and compile errors on nightly (#6886)

Nightly has added a bunch of compiler and linter warnings. There is also
two dependencies that fail compilation on latest nightly due to using
the old `stdsimd` feature name. This PR fixes them.

libs/utils/src/sync/heavier_once_cell.rs

@@ -239,7 +239,6 @@ mod tests {
     use std::{
         convert::Infallible,
         pin::{pin, Pin},
-        sync::atomic::{AtomicUsize, Ordering},
         time::Duration,
     };