pad function
Implementation
VARP pad(VARP x, List<int> padWidth, {F.PadValueMode mode = F.PadValueMode.CONSTANT}) {
final ndim = x.ndim;
MnnAssert(ndim != null, "x must have a shape");
var padWidth_ = asarray<int32>(padWidth);
MnnAssert(padWidth_.dtype == HalideType.i32, "padWidth must be int32");
padWidth_ = broadcastTo(padWidth_, [ndim!, 2]);
return F.pad(x, padWidth_, mode: mode);
}