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/dropdown/operation.rs

@@ -2,9 +2,6 @@
 // SPDX-License-Identifier: MPL-2.0 AND MIT
 //! Operate on dropdown widgets.
 
-use super::State;
-use iced::Rectangle;
-use iced_core::widget::{Id, Operation};
 
 pub trait Dropdown {
     fn close(&mut self);