Add rustfmt.toml for explicit styling (#348)

* Propose an explicit .rustfnt.toml
Use 2024 style, 4 spaces for tabs and epand the default width a tad

* Auto-format the existing code with new rules

lan-mouse-gtk/src/authorization_window/imp.rs

@@ -4,8 +4,9 @@ use adw::prelude::*;
 use adw::subclass::prelude::*;
 use glib::subclass::InitializingObject;
 use gtk::{
+    Button, CompositeTemplate, Label,
     glib::{self, subclass::Signal},
-    template_callbacks, Button, CompositeTemplate, Label,
+    template_callbacks,
 };
 
 #[derive(CompositeTemplate, Default)]