Apply Symfony code style conventions

Co-authored-by: OskarStark <995707+OskarStark@users.noreply.github.com>

Author: Copilot

src/agent/src/Toolbox/StreamResult.php

@@ -42,7 +42,7 @@ public function getContent(): \Generator
                 // Strings are iterable in PHP but yield from would iterate character-by-character.
                 // We need to yield the complete string as a single value to preserve streaming behavior.
                 // null should also be yielded as-is.
-                if (is_string($content) || $content === null || !is_iterable($content)) {
+                if (\is_string($content) || null === $content || !is_iterable($content)) {
                     yield $content;
                 } else {
                     yield from $content;