style: apply php-cs-fixer and PHPStan fixes (#289)

* style: apply php-cs-fixer to test files

Addresses drift flagged by the default PHP-CS-Fixer config — mostly
adds missing `: void` return types on pre-existing test methods.

No behavioural changes.

* fix: resolve phpstan errors surfaced by qa

- Drop the obsolete `Method ::test*() has no return type specified`
  ignore rule — every test method now declares a return type, so
  the pattern never matches and phpstan reports it as unmatched.
- Remove `?? []` from two reads of `CallToolRequest::$arguments`;
  the property is typed `array` (non-nullable), so the coalesce is
  a no-op that phpstan flags.

---------

Co-authored-by: DDEV User <nobody@example.com>

tests/Unit/Schema/JsonRpc/RequestTest.php

@@ -16,7 +16,7 @@ use PHPUnit\Framework\TestCase;
 
 final class RequestTest extends TestCase
 {
-    public function testMetaAndIdAreLoopedThrough()
+    public function testMetaAndIdAreLoopedThrough(): void
     {
         $requestImplementation = new class extends Request {
             public static function getMethod(): string