fix(lifecycle): use process group kill (-pid) in handleExit safety net

With detached:true children, the synchronous exit handler must kill
the entire process group, not just the direct PID.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@push.rocks/smartexit",
-  "version": "2.0.1",
+  "version": "2.0.2",
   "private": false,
   "description": "A library for managing graceful shutdowns of Node.js processes by handling cleanup operations, including terminating child processes.",
   "main": "dist_ts/index.js",