feat: add type validation for IO.read prompt and stdin support in test runner

Add string type check for IO.read() prompt argument with Fiber.abort on non-string input. Implement stdin piping in test runner via // stdin: comments, allowing tests to provide input lines. Update stack trace filtering to omit built-in library frames with empty source paths. Add io/read.wren and io/read_arg_not_string.wren test cases.

src/wren_core.c

@@ -1202,7 +1202,7 @@ void wrenInitializeCore(WrenVM* vm)
   vm->numClass->name->obj.classObj = vm->stringClass;
   vm->stringClass->name->obj.classObj = vm->stringClass;
 
-  wrenInterpret(vm, "Wren core library", libSource);
+  wrenInterpret(vm, "", libSource);
 
   vm->listClass = AS_CLASS(findGlobal(vm, "List"));
   NATIVE(vm->listClass->obj.classObj, " instantiate", list_instantiate);