feat(tvix/eval): wrap Closure in Rc<> to match cppnix semantics

Change-Id: I595087eff943d38a9fc78a83d37e207bb2ab79bc
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7443
Reviewed-by: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI

tvix/eval/src/compiler/mod.rs

@@ -948,7 +948,7 @@ impl Compiler<'_> {
                 if is_suspended_thunk {
                     Value::Thunk(Thunk::new_suspended(lambda, span))
                 } else {
-                    Value::Closure(Closure::new(lambda))
+                    Value::Closure(Rc::new(Closure::new(lambda)))
                 },
                 node,
             );