fix: clean up scoped autoloaders during arch scans

[nkgotcode]

Fix arch object scanning so temporary Composer autoloaders registered while resolving object descriptions are cleaned up after the callback completes.

This prevents Rector-related autoload state discovered during an arch scan from leaking into later tests in the same process.

Fixes pestphp/pest#1732.

Validation:

docker run --rm -e COMPOSER_ROOT_VERSION=4.x-dev -v "$PWD":/app -w /app composer:2 sh -lc 'git config --global --add safe.directory /app && composer install --no-interaction --prefer-dist'
docker run --rm -e COMPOSER_ROOT_VERSION=4.x-dev -v "$PWD":/app -w /app php:8.4-cli php vendor/bin/pest tests/Composer.php --filter 'removes composer loaders registered during a callback' --compact
docker run --rm -e COMPOSER_ROOT_VERSION=4.x-dev -v "$PWD":/app -w /app php:8.4-cli php vendor/bin/pint --test src/Support/Composer.php src/Factories/ObjectDescriptionFactory.php tests/Composer.php
docker run --rm -e COMPOSER_ROOT_VERSION=4.x-dev -v "$PWD":/app -w /app php:8.4-cli php -d memory_limit=-1 vendor/bin/phpstan analyse --ansi