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>

src/Server/Handler/Request/CallToolHandler.php

@@ -58,7 +58,7 @@ final class CallToolHandler implements RequestHandlerInterface
         \assert($request instanceof CallToolRequest);
 
         $toolName = $request->name;
-        $arguments = $request->arguments ?? [];
+        $arguments = $request->arguments;
 
         $this->logger->debug('Executing tool', ['name' => $toolName, 'arguments' => $arguments]);