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

apps/labrinth/src/models/v3/projects.rs

@@ -122,7 +122,7 @@ pub fn from_duplicate_version_fields(
     }
 
     // Remove duplicates
-    for (_, v) in fields.iter_mut() {
+    for v in fields.values_mut() {
         *v = mem::take(v).into_iter().unique().collect_vec();
     }
     fields