fix: showTimeSelect now works with selectsRange (#4332)

[martijnrusschen]

Fixes #4332

• Modified handleTimeChange to properly handle range mode
• When only startDate is selected, time is applied to startDate
• When both dates are selected, time is applied to endDate
• onChange is called with proper [Date, Date] tuple format
• Added 6 tests for the fix

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.22%. Comparing base (649af62) to head (0d7812f).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6074   +/-   ##
=======================================
  Coverage   99.22%   99.22%           
=======================================
  Files          30       30           
  Lines        3597     3612   +15     
  Branches     1543     1531   -12     
=======================================
+ Hits         3569     3584   +15     
  Misses         27       27           
  Partials        1        1           

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