Method copy

include/wasm.hh:126–130

  }

  auto copy() const -> vec {
    auto v = vec(size_);
    if (v) for (size_t i = 0; i < size_; ++i) v.data_[i] = data_[i];
    return v;
  }

  // TODO: This can't be used for e.g. vec<Val>
  auto deep_copy() const -> vec {