fix(DatePicker): correct ISO week number calculation

[Coderxrohan]

Problem:
The calendar week number was calculated incorrectly around year boundaries, causing the second calendar week to be shown as Week 1 instead of following the ISO-8601 standard.

Impact:
This resulted in incorrect week labels in the DatePicker, leading to confusion for users relying on week-based planning, particularly in late December and early January.

Solution:
The getWeekNumber logic was updated to use an ISO-8601 compliant, UTC-based calculation, ensuring correct Week 1 handling and accurate week numbering across year transitions.

Fixes #6277 (Calendar: every calendar week is wrong)

[Coderxrohan]

@mertsincan & @tugcekucukoglu
Can you please verify once the changes are done in right direction.