Read the update header once per request, not on every page load

The filter is registered on every request a shop serves, not just in wp-admin,
and get_file_data() opens and scans the plugin file each time it is asked.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

includes/class-updater.php

@@ -57,15 +57,30 @@ class WC_EDM_Updater {
 		add_action( 'upgrader_process_complete', array( $this, 'forget' ), 10, 0 );
 	}
 
+	/**
+	 * Memoised update URI, so the plugin file is read at most once a request.
+	 *
+	 * @var string|null
+	 */
+	private static $uri = null;
+
 	/**
 	 * The repository this plugin updates from, as stated in its own header.
 	 *
+	 * Read from the header rather than a constant so that there is exactly one
+	 * place saying where updates come from — but memoised, because the filter
+	 * is registered on every request a shop serves, not just in wp-admin, and
+	 * get_file_data() opens and scans the file each time it is asked.
+	 *
 	 * @return string
 	 */
 	public static function update_uri() {
-		$data = get_file_data( WC_EDM_PLUGIN_FILE, array( 'uri' => 'Update URI' ) );
+		if ( null === self::$uri ) {
+			$data      = get_file_data( WC_EDM_PLUGIN_FILE, array( 'uri' => 'Update URI' ) );
+			self::$uri = isset( $data['uri'] ) ? trim( $data['uri'] ) : '';
+		}
 
-		return isset( $data['uri'] ) ? trim( $data['uri'] ) : '';
+		return self::$uri;
 	}
 
 	/**