fix: Update plugin header version to 0.4.3

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

wp-prometheus.php

@@ -3,7 +3,7 @@
  * Plugin Name: WP Prometheus
  * Plugin URI: https://src.bundespruefstelle.ch/magdev/wp-prometheus
  * Description: Prometheus metrics endpoint for WordPress with extensible hooks for custom metrics.
- * Version: 0.4.2
+ * Version: 0.4.3
  * Requires at least: 6.4
  * Requires PHP: 8.3
  * Author: Marco Graetsch