boost::heap::skew_heap improperly handles rvalue_reference when creating a node.

The `skew_heap_node` constructor taking an rvalue reference [makes a copy](https://github.com/boostorg/heap/blob/19fda03545e1b85b3a2d3a94b9a3930ec64335d4/include/boost/heap/skew_heap.hpp#L92-L93) instead of moving it in. This prevents the use of move only types with `skew_heap`.

I'm pretty sure that you just need to add `std::move` to the initializer list construction. E.g.
```
skew_heap_node(value_type && v):
value(std::move(v))
```

Inspect boost/heap/skew_heap.hpp at lines 92–93, starting with the skew_heap_node constructor that takes an rvalue reference. Confirm the constructor preserves move-only values rather than copying them; done means skew_heap can be instantiated with move-only types without this construction failure.

Written by the indexing model from the issue text.