Do not use fast lookup for frames.

Fast lookup is not possible since mjOBJ_FRAME > mjNOBJECT, which is the size of the objects maps used for the search.

Fixes #2328.

PiperOrigin-RevId: 712479460
Change-Id: I7bcfa75ff8a1e288183d60ed4a44cab5bc6f4173

test/user/user_api_test.cc

@@ -1014,6 +1014,9 @@ TEST_F(MujocoTest, AttachDifferent) {
   mjModel* m_attached = mj_compile(parent, 0);
   EXPECT_THAT(m_attached, NotNull());
 
+  // check frame is present
+  EXPECT_THAT(mjs_findFrame(parent, "frame"), NotNull());
+
   // check full name stored in mjModel
   EXPECT_STREQ(mj_id2name(m_attached, mjOBJ_BODY, 2), "attached-body-1");