Use bitmask cast instead of a round trip to&from bitmask

Author: farnoy

crates/core_simd/src/vector.rs

@@ -1156,5 +1156,5 @@ where
 {
     let index = lane_indices::<i8, N>();
     let lt = index.simd_lt(Simd::splat(i8::try_from(len).unwrap_or(i8::MAX)));
-    Mask::<M, N>::from_bitmask_vector(lt.to_bitmask_vector())
+    lt.cast()
 }