Add PHPUnit 12 support and fix test compatibility issues

[tkaratug]

Summary

This PR adds support for PHPUnit 12 and fixes test compatibility issues that arose from updates to the underlying php-mcp/server package.

Changes Made

1. PHPUnit Version Support

• Updated composer.json to support PHPUnit 12 alongside existing versions 10 and 11
• Changed constraint from ^10.0 || ^11.0 to ^10.0 || ^11.0 || ^12.0

2. Test Fixes

• Fixed failing tests in ManualRegistrationTest.php that were caused by API changes in php-mcp/server v3.2.1
• Updated test assertions to use the new handler property instead of deprecated handlerClass and handlerMethod properties
• The registered elements now store handler information in a single handler property that can contain:
  • Array format: [ClassName::class, 'methodName'] for class methods
  • String format: ClassName::class for invokable classes

Testing

• All 26 tests now pass successfully
• No breaking changes to existing functionality
• Maintains backward compatibility

Motivation

This update ensures the package works with the latest PHPUnit version and remains compatible with recent updates to the php-mcp/server dependency.

[CodeWithKyrian]

Thank you!