Add Laravel 13 support

[swilla]

Summary

• allow illuminate/contracts 13.x in addition to existing Laravel 10-12 support
• allow Testbench 11 and Pest 4 for Laravel 13 verification
• add PHP 8.4 to the GitHub Actions test matrix

Verification

• composer validate --strict
• composer update --with='illuminate/contracts:13.*' --with='orchestra/testbench:11.*' --no-interaction --prefer-dist --no-progress
• composer test with Laravel 13.15.0, Filament 5.6.7, Testbench 11.1.0, Pest 4.7.3

Note

• composer analyse is not part of this repo's current GitHub Actions workflow. When run locally against the Laravel 13 / PHPStan 2 dependency set, it exposes existing PHPStan configuration/type issues unrelated to the Composer support bump.