Release 7.0.0

[ppeble]

Bumps VERSION.txt to 7.0.0 and adds the matching CHANGELOG.md entry to trigger an automated release.

Major release: drops support for EOL Ruby 3.2 (endoflife.date/ruby), raising the minimum supported version to Ruby 3.3.

• Drop support for EOL Ruby 3.2; minimum supported version is now Ruby 3.3 (testing 3.3, 3.4, 4.0, ruby-head)
• Fix nz Canterbury Anniversary Day to the second Friday after the first Tuesday of November (holidays#285)
• Fix lu Whit Monday to fall on Monday (Easter Sunday + 50 days) instead of Sunday (holidays#289)
• Replace nil-returning year-gate functions with year_ranges
• Clarify that formal holidays are what is commonly called statutory holidays