qa: check parsed multipath descriptors dont share references

There's no need for it to be a shared_ptr.

src/script/miniscript.h

@@ -186,7 +186,7 @@ using Opcode = std::pair<opcodetype, std::vector<unsigned char>>;
 template<typename Key> struct Node;
 template<typename Key> using NodeRef = std::unique_ptr<const Node<Key>>;
 
-//! Construct a miniscript node as a shared_ptr.
+//! Construct a miniscript node as a unique_ptr.
 template<typename Key, typename... Args>
 NodeRef<Key> MakeNodeRef(Args&&... args) { return std::make_unique<const Node<Key>>(std::forward<Args>(args)...); }
 
@@ -1688,7 +1688,7 @@ public:
     template <typename Ctx> Node(const Ctx& ctx, Fragment nt, uint32_t val = 0)
         : Node(internal::NoDupCheck{}, ctx.MsContext(), nt, val) { DuplicateKeyCheck(ctx); }
 
-    // Delete copy constructor and assignment operator
+    // Delete copy constructor and assignment operator, use Clone() instead
     Node(const Node&) = delete;
     Node& operator=(const Node&) = delete;
 };