Geometry Nodes: add assert to check if node supports lazyness

Only nodes supporting lazyness can mark inputs as unused. For other
nodes, this is done automatically of all outputs are unused.

Differential Revision: https://developer.blender.org/D15409

source/blender/modifiers/intern/MOD_nodes_evaluator.cc

@@ -1863,6 +1863,7 @@ bool NodeParamsProvider::lazy_require_input(StringRef identifier)
 
 void NodeParamsProvider::set_input_unused(StringRef identifier)
 {
+  BLI_assert(node_supports_laziness(this->dnode));
   const DInputSocket socket = this->dnode.input_by_identifier(identifier);
   BLI_assert(socket);