[ 2026-02-13; LWG telecon. ]

Setting priority to P2, after P3932R0 (Fix LWG4470: Fix integer-from in [simd]), resolving the issue was accepted on telecon.

The return type of `simd::cat` is defined using deduce-abi-t rather than `resize_t`. This can lead to:

basic_vec<T, Abi> x = […]
auto [...vs] = simd::chunk<2>(x);
auto y = simd::cat(vs...);
static_assert(is_same_v<decltype(x), decltype(y)>); // can fail