Use string traces in ForEach ordering integration tests

Replace numeric accumulation (ModVarScene) with string concatenation
(ModVarSceneTxt) in all orderBy/limit tests to make the exact iteration
order and values visible in the assertion. This makes test failures much
easier to diagnose since the full trace is a readable string like
"10;20;30;50;" rather than a single sum.

Also add gdjs.evtTools.common.toString to the GDJS mock so that
ToString() expressions work in code-generation integration tests.

https://claude.ai/code/session_01LXTeNz7ehNS5TqFYSU6aw5

Author: claude

GDevelop.js/TestUtils/GDJSMocks.js

@@ -1035,6 +1035,7 @@ function makeMinimalGDJSMock(options) {
         },
         common: {
           resolveAsyncEventsFunction: ({ task }) => task.resolve(),
+          toString: (num) => '' + num,
         },
       },
       registerBehavior: (behaviorTypeName, Ctor) => {