logger: add a dedicated QML logging Singleton

- adds log.info/error/debug/warn/fatal
- adds ability to write logs to any file
- add CLI options in addition to env to set log levels

quickshell/Widgets/PluginGlobalVar.qml

@@ -3,24 +3,25 @@ import qs.Services
 
 Item {
     id: root
+    readonly property var log: Log.scoped("PluginGlobalVar")
 
     required property string varName
     property var defaultValue: undefined
 
     readonly property var value: {
-        const pid = parent?.pluginId ?? ""
+        const pid = parent?.pluginId ?? "";
         if (!pid || !PluginService.globalVars[pid]) {
-            return defaultValue
+            return defaultValue;
         }
-        return PluginService.globalVars[pid][varName] ?? defaultValue
+        return PluginService.globalVars[pid][varName] ?? defaultValue;
     }
 
     function set(newValue) {
-        const pid = parent?.pluginId ?? ""
+        const pid = parent?.pluginId ?? "";
         if (pid) {
-            PluginService.setGlobalVar(pid, varName, newValue)
+            PluginService.setGlobalVar(pid, varName, newValue);
         } else {
-            console.warn("PluginGlobalVar: Cannot set", varName, "- no pluginId from parent")
+            log.warn("Cannot set", varName, "- no pluginId from parent");
         }
     }