fix(tvix/eval): address current clippy lints

Note that I've allowed `needless_lifetimes` for the attribute set
iterator, as I find the type easier to understand with these
annotations present.

Change-Id: I33abb17837ee4813076cdb9a87f54bac4a37044e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6373
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

tvix/eval/src/vm.rs

@@ -527,7 +527,6 @@ impl VM {
     fn resolve_dynamic_upvalue(&mut self, ident_idx: ConstantIdx) -> EvalResult<Value> {
         let chunk = self.chunk();
         let ident = chunk.constant(ident_idx).as_str()?.to_string();
-        drop(chunk); // some lifetime trickery due to cell::Ref
 
         // Peek at the current instruction (note: IP has already
         // advanced!) to see if it is actually data indicating a