chore(clippy): enable and fix many stricter lints (#3783)

* chore(clippy): enable and fix many stricter lints

These ensure that the codebase uses more idiomatic, performant, and
concise language constructions.

* chore: make non-Clippy compiler warnings also deny by default

packages/app-lib/src/api/pack/import/curseforge.rs

@@ -65,8 +65,7 @@ pub async fn import_curseforge(
         "Curseforge-{}",
         curseforge_instance_folder
             .file_name()
-            .map(|a| a.to_string_lossy().to_string())
-            .unwrap_or("Unknown".to_string())
+            .map_or("Unknown".to_string(), |a| a.to_string_lossy().to_string())
     );
 
     let state = State::get().await?;