Add tabbing focus support to Calendar and DatePicker components

[cheton]

Currently, the Calendar and DatePicker components only support focus-visible state for the Previous month and Next month arrow buttons. Current implementation does not support tabbing focus for date selection, which can impact keyboard navigation and accessibility.

[cheton]

The following accessibility issues need to be addressed, as they are currently unresolved in PR #903.

await testA11y(container, {
  axeOptions: {
    rules: {
      // FIXME: Certain ARIA roles must contain particular children (aria-required-children)"
      'aria-required-children': { enabled: false },

      // FIXME: Interactive controls must not be nested (nested-interactive)
      'nested-interactive': { enabled: false },
    },
  },
});