Add support for Laravel 13

- Allow illuminate/contracts ^13.0
- Allow orchestra/testbench ^11.0 and Pest 4 (with plugins) for dev
- Add Laravel 13 to the CI test matrix
- Update requirements in README

README.md

@@ -9,7 +9,7 @@ A Laravel package for proxying Plausible Analytics, improving performance and pr
 
 ## Requirements
 
-- Laravel 11 or 12
+- Laravel 11, 12 or 13
 - PHP 8.3 or 8.4
 
 ## Installation