chore: More cleanup after cargo clippy

Also added some type efficiency improvements (using references where possible and added SliceDeque crate)

Signed-off-by: quexeky <git@quexeky.dev>

src-tauri/src/download_manager/mod.rs

@@ -4,6 +4,5 @@ pub mod download_manager_builder;
 pub mod download_thread_control_flag;
 pub mod downloadable;
 pub mod downloadable_metadata;
-pub mod generate_downloadable;
 pub mod progress_object;
 pub mod queue;