validate substituted node type in instantiateTreeNode

[aysha-afrah26]

Substitution rules replace a node by ID, but instantiateTreeNode never checks that the replacement has a compatible node type. The XML around the node was validated for its ORIGINAL type (mandatory ID, child count), so a compact leaf swapped for a structural node is mishandled at build time:

<AlwaysSuccess name="action_A"/>  +  addSubstitutionRule("action_A", "SubTree")
=> Segmentation fault (exit 139)

The crash is std::string(element->Attribute("ID")) at xml_parsing.cpp:1095. A compact <AlwaysSuccess/> carries no ID, so Attribute("ID") is null and the string constructor calls strlen(nullptr). The same setup with "Inverter" leaves the decorator child_node_ null and segfaults on the first tick instead. Both are reachable from an untrusted SubstitutionRules JSON plus ordinary XML, before any node runs.

The fix rejects a substitution whose resulting type differs from the original unless the replacement is a leaf (Action or Condition). That keeps the supported cases working, same-type swaps and the SubTree to TestNode mocking path from #934, and turns both crashes into a clear RuntimeError. Added a regression test that segfaults before the change and passes after.