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>

examples/server/custom-method-handlers/CallToolRequestHandler.php

@@ -44,7 +44,7 @@ class CallToolRequestHandler implements RequestHandlerInterface
         \assert($request instanceof CallToolRequest);
 
         $name = $request->name;
-        $args = $request->arguments ?? [];
+        $args = $request->arguments;
 
         if (!isset($this->toolDefinitions[$name])) {
             return new Error($request->getId(), Error::METHOD_NOT_FOUND, \sprintf('Tool not found: %s', $name));