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

filter_plugins/get_service_name.py

@@ -1,23 +1,36 @@
-# filter_plugins/get_service_name.py
 """
 Custom Ansible filter to build a systemctl unit name (always lowercase).
 
 Rules:
 - If `systemctl_id` ends with '@': drop the '@' and return
-  "{systemctl_id_without_at}.{software_name}@.{suffix}".
-- Else: return "{systemctl_id}{software_name}.{suffix}".
+  "{systemctl_id_without_at}.{software_name}@{suffix_handling}".
+- Else: return "{systemctl_id}.{software_name}{suffix_handling}".
+
+Suffix handling:
+- Default "" → automatically pick:
+    - ".service" if no '@' in systemctl_id
+    - ".timer"  if '@' in systemctl_id
+- Explicit False → no suffix at all
+- Any string → ".{suffix}" (lowercased)
 """
 
-def get_service_name(systemctl_id, software_name, suffix="service"):
+def get_service_name(systemctl_id, software_name, suffix=""):
     sid = str(systemctl_id).strip().lower()
     sw  = str(software_name).strip().lower()
-    sfx = str(suffix).strip().lower()
 
-    if sid.endswith('@'):
-        base = sid[:-1]  # drop the trailing '@'
-        return f"{base}.{sw}@.{sfx}"
+    # Determine suffix
+    if suffix is False:
+        sfx = ""  # no suffix at all
+    elif suffix == "" or suffix is None:
+        sfx = ".timer" if sid.endswith("@") else ".service"
     else:
-        return f"{sid}.{sw}.{sfx}"
+        sfx = "." + str(suffix).strip().lower()
+
+    if sid.endswith("@"):
+        base = sid[:-1]  # drop the trailing '@'
+        return f"{base}.{sw}@{sfx}"
+    else:
+        return f"{sid}.{sw}{sfx}"
 
 
 class FilterModule(object):