refactor: improve get_service_name suffix handling and handler usage

- Updated filter_plugins/get_service_name.py:
  * Default suffix handling: auto-select .service (no '@') or .timer (with '@')
  * Explicit False disables suffix entirely
  * Explicit string suffix still supported
- Updated sys-systemctl handler to use new filter instead of SYS_SERVICE_SUFFIX
- Extended unit tests to cover new suffix behavior

Ref: https://chat.openai.com/share/8c2de9e6-daa0-44dd-ae13-d7a7d8d8b6d9

roles/sys-systemctl/handlers/main.yml

@@ -1,6 +1,6 @@
 - name: "refresh systemctl service"
   systemd:
-    name: "{{ systemctl_id }}{{ SYS_SERVICE_SUFFIX }}"
+    name: "{{ systemctl_id | get_service_name(SOFTWARE_NAME) }}"
     daemon_reload: yes
     enabled: yes
     state: "{{ systemctl_state }}"