[Perf/Refactor] Performance improved for CU-related scrolling + Minor refactoring
[Refactor] Minor - explicitly call `updateCUsAndRelatedState` on DOM ready defined in mod_CUsMgr
(was being called in mod_CUsMgr's `setup` which was being called by mod_main on dom ready.)
[Minor] Ensure checkOverlayCssHasTransition() returns false instead of 0