treewide: enforce strict clippy check

fix-vm/src/primops/conv.rs

@@ -27,6 +27,10 @@ pub fn to_string<'gc, M: Machine<'gc>>(
     )))
 }
 
+#[expect(
+    clippy::unreachable,
+    reason = "val was forced to WHNF by force_and_retry, so its type is never Thunk here"
+)]
 pub fn type_of<'gc, M: Machine<'gc>>(
     m: &mut M,
     ctx: &mut impl VmRuntimeCtx,