yoda: cargo fix --lib (libcosmic-yoda) — drop 99 trivial warnings

Auto-applied suggestions on libcosmic-yoda lib only: unused imports,
unused-by-name params (prefixed with _), redundant mutability. From 113
warnings down to 14 (the 14 remaining are real signals: never-read
fields, unreachable patterns, etc., to be reviewed manually).

Leyoda 2026 – GPLv3

src/widget/dnd_source.rs

@@ -8,8 +8,7 @@ use crate::{
 };
 use iced::{
     Event, Length, Point, Rectangle, Vector,
-    clipboard::dnd::{DndAction, DndEvent, SourceEvent},
-    event, mouse, overlay,
+    clipboard::dnd::{DndAction, DndEvent, SourceEvent}, mouse, overlay,
 };
 use iced_core::{
     self, Clipboard, Shell, layout, renderer,