fix: TypeScript type improvements for DatePicker props

[martijnrusschen]

Summary

This PR fixes two TypeScript type issues:

1. Property 'minDate' does not exist on type 'IntrinsicAttributes & ((Partial<Pick<Omit<CalendarProps,.... #6143 - minDate and maxDate props not available in TypeScript types
2. selectsMultiple - Type 'boolean | undefined' is not assignable to type 'true'. #6131 - selectsMultiple type error when spreading props

Changes

Fix for minDate/maxDate (#6143)

• Updated CalendarProps to use YearDropdownProps (optional) instead of MonthYearDropdownProps (required) for minDate/maxDate
• Made minDate/maxDate optional in MonthYearDropdownOptionsProps
• Added default date range (±5 years) when minDate/maxDate not provided for MonthYearDropdown components

Fix for selectsRange/selectsMultiple spreading (#6131)

• Changed selectsRange and selectsMultiple from required literal true to optional true in the union type branches
• This allows spreading props where these values might be boolean | undefined (e.g., from wrapper components using Omit<DatePickerProps, 'onChange'>)
• Added internal type aliases (OnChangeSingle, OnChangeRange, OnChangeMultiple) and type assertions to maintain type safety
• Updated test files to use explicit type annotations for onChange callbacks

Root Causes

#6143

In CalendarProps, the union type for showMonthYearDropdown was using Pick<MonthYearDropdownProps, "maxDate" | "minDate"> which inherited required minDate/maxDate. This caused TypeScript to not properly expose these props.

#6131

The selectsRange: true and selectsMultiple: true were typed as required literal types. When users spread DatePickerProps (e.g., Omit<DatePickerProps, 'onChange'>), these become boolean | undefined, which couldn't be assigned to the literal true.

Fixes #6143
Fixes #6131

Test plan

• All 1445 existing tests pass
• TypeScript type-check passes
• Linter passes

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.26%. Comparing base (8b66e0d) to head (3a82fd1).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6156   +/-   ##
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  Coverage   99.25%   99.26%           
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  Files          30       30           
  Lines        3783     3792    +9     
  Branches     1627     1631    +4     
=======================================
+ Hits         3755     3764    +9     
  Misses         27       27           
  Partials        1        1           

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