roblox_emulator: implement __newindex Instance

lib/roblox_emulator/src/runner/instance/instance.rs

@@ -345,6 +345,11 @@ impl mlua::UserData for Instance{
 						let typed_value=value.as_str().ok_or_else(||mlua::Error::runtime("Expected string"))?.to_owned();
 						rbx_types::Variant::ContentId(typed_value.into())
 					},
+					rbx_reflection::DataType::Value(rbx_types::VariantType::Ref)=>{
+						// why clone?
+						let typed_value=Option::<Instance>::from_lua(value.clone(),lua)?;
+						rbx_types::Variant::Ref(typed_value.map_or(Ref::none(),|instance|instance.referent))
+					},
 					other=>return Err(mlua::Error::runtime(format!("Unimplemented property type: {other:?}"))),
 				};
 				// the index is known to be a real property at this point