fix: eliminate PHPUnit warnings and deprecations in test suite

Set defaultTestSuite="CoreCore" to prevent 222 duplicate file warnings,
and replace deprecated isType() with isArray()/isString() in notification
listener tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

phpunit.xml

@@ -2,7 +2,8 @@
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/11.0/phpunit.xsd"
          bootstrap="tests/bootstrap.php"
-         colors="true">
+         colors="true"
+         defaultTestSuite="CoreCore">
     <source ignoreIndirectDeprecations="true">
         <include>
             <directory>config</directory>