Move wp-cli/package-command from require to require-dev

This change removes package-command and its 20+ dependencies (including
composer/composer) from production installations while keeping it
available for:
- Phar builds (built with dev dependencies)
- Development environments
- Users who explicitly install it

Reduces the dependency count from 64 to 38 packages when installing
wp-cli-bundle in a project via Composer.

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>

Author: Copilot

composer.json

@@ -27,7 +27,6 @@
     "wp-cli/language-command": "^2",
     "wp-cli/maintenance-mode-command": "^2",
     "wp-cli/media-command": "^2",
-    "wp-cli/package-command": "^2.1",
     "wp-cli/rewrite-command": "^2",
     "wp-cli/role-command": "^2",
     "wp-cli/scaffold-command": "^2",
@@ -40,10 +39,12 @@
   },
   "require-dev": {
     "roave/security-advisories": "dev-latest",
+    "wp-cli/package-command": "^2.1",
     "wp-cli/wp-cli-tests": "^5"
   },
   "suggest": {
-    "psy/psysh": "Enhanced `wp shell` functionality"
+    "psy/psysh": "Enhanced `wp shell` functionality",
+    "wp-cli/package-command": "Manage WP-CLI packages (included in Phar builds, needed for package management when using Composer-based installation)"
   },
   "config": {
     "allow-plugins": {