Hi,

We're heavily using the Scheduler component, but we've hit a problem with `slotClick` in scenarios involving multiple scheduler instances on the same page.

With two schedulers on one page, slot detection for the second scheduler (used in context-menu flows via slotByPosition) can be wrong.

Detaild repro: Stackblitz

Repro steps:
- Right-click any slot in Scheduler #2.
- slotClick gives expected slot, but slotByPosition(...) can resolve incorrectly/undefined, which can cause error in the app when code depends on slotByPosition.

The issue:
- BaseSlotService.calculateScaleX() uses document.querySelector(".k-scheduler"), which always picks the first scheduler in DOM.
- With two schedulers on one page, slot detection for the second scheduler (used in context-menu flows via slotByPosition) can be wrong.
- Relevant code:
const h = document.querySelector(".k-scheduler");
return h.getBoundingClientRect().width / h.offsetWidth;
- Expected: the instance of scheduler used in the calculation should be the one that fired event, not the first one from DOM.