[Demo] Remove unused nyholm/nsa dependency

The nyholm/nsa library was declared as a dev dependency but not used anywhere
in the codebase. Standard PHP reflection is used instead for accessing private
properties in tests.

Author: OskarStark

demo/composer.json

@@ -56,7 +56,6 @@
         "symfony/symfony": "*"
     },
     "require-dev": {
-        "nyholm/nsa": "^1.3",
         "php-cs-fixer/shim": "^3.75",
         "phpstan/phpstan": "^2.1",
         "phpunit/phpunit": "^11.5",