fix(tvix/eval): fix current clippy warnings

It's been a while since the last time, so quite a lot of stuff has
accumulated here.

Change-Id: I0762827c197b30a917ff470fd8ae8f220f6ba247
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7597
Reviewed-by: grfn <grfn@gws.fyi>
Autosubmit: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

tvix/eval/src/value/function.rs

@@ -30,7 +30,7 @@ impl Formals {
         Q: ?Sized + Hash + Eq,
         NixString: std::borrow::Borrow<Q>,
     {
-        self.ellipsis || self.arguments.contains_key(&arg)
+        self.ellipsis || self.arguments.contains_key(arg)
     }
 }