Replace custom URI/URL validation with simplesamlphp/assert

[kayjoosten]

Summary

• add simplesamlphp/assert and use it for legacy URI/URL validation
• keep the legacy URI parser helper for compatibility while switching validation to SimpleSAML\Assert
• update legacy validator tests to cover the migrated behavior

Verification

• ./vendor/bin/phpcs --standard=ci/qa-config/phpcs-legacy.xml --extensions=php library/EngineBlock/Validator/Uri.php library/EngineBlock/Attributes/Validator/Type.php tests/library/EngineBlock/Test/Validator/UriTest.php tests/library/EngineBlock/Test/Attributes/Validator/TypeTest.php
• XDEBUG_MODE=coverage ./vendor/bin/phpunit --configuration=./tests/phpunit.xml tests/library/EngineBlock/Test/Validator/UriTest.php tests/library/EngineBlock/Test/Attributes/Validator/TypeTest.php
• XDEBUG_MODE=coverage ./vendor/bin/phpunit --configuration=./tests/phpunit.xml --testsuite=unit
• XDEBUG_MODE=coverage ./vendor/bin/phpunit --configuration=./tests/phpunit.xml tests/library/

Notes

• I also ran the default Behat suite in Docker and investigated failures. It still fails broadly in unrelated UI/authentication flow paths after fixing a stale Symfony cache issue, which looks like an existing baseline/environment problem rather than a regression from this validator change.