Add split range picker via rangeEnd() (RFC 0001)

[coolsam726]

Summary

• Adds RFC 0001 and ->rangeEnd('ends_at') so one range picker reads/writes separate start/end model attributes
• Supports datetime ranges with ->time() and custom formats; end times are preserved on save
• Sorts inverted same-day datetime selections chronologically in JS and PHP so the earlier time always becomes the start
• Expands rangeEnd hydration, sync, and dehydration tests to 100% coverage (151 tests)

RFC

Closes RFC 0001.

API

Flatpickr::make('starts_at')
    ->rangePicker()
    ->rangeEnd('ends_at')
    ->time()
    ->format('Y-m-d H:i');

Default single-field array behaviour is unchanged when rangeEnd() is omitted.

Test plan

• vendor/bin/pest --coverage --min=96 — 151 tests pass, 100% coverage
• Open a form with ->rangePicker()->rangeEnd('ends_at')->time(), select a datetime range, save, and confirm both columns persist with correct times
• Select same-day inverted times (e.g. 6:30am then 6:10am) and confirm the picker/state reorder to 6:10am → 6:30am
• Edit an existing record and confirm the picker shows the saved range

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a7c23a5) to head (332a03b).
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Additional details and impacted files

@@             Coverage Diff              @@
##                main      #153    +/-   ##
============================================
  Coverage     100.00%   100.00%            
- Complexity       293       354    +61     
============================================
  Files              6         6            
  Lines            698       823   +125     
============================================
+ Hits             698       823   +125     

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