VCS {N{x}}==K returns 0 only when K is unreachable

Before reporting a simulator X-semantics bug where {N{en}} == const gives 0 instead of IEEE's x, test reachable vs unreachable constants. VCS (2020.12-2024.09) returned 0 only for patterns impossible for N copies of one bit (e.g. 4'b0101, 4'b0001) and x for reachable ones (4'b1111, 4'b0000, mixed {{2{en}},2'b01}==4'b1101) across 816 runs incl. dump/debug modes, flops and case. So it is correlation-aware non-LRM behaviour (physically exact), not an X-hiding bug; still inconsistent since != stays x and the written-out {en,en,en,en} form usually is not optimized. A human pointing out 'x could be 1 so it could be true' prompted the decisive test.