feat(tvix/eval): wrap Closure::upvalues in Rc

See cl/7372; Nix equality semantics require the ability to track
pointer equality of upvalue-sets.

Signed-off-by: Adam Joseph <adam@westernsemico.com>
Change-Id: I82ba517499cf370189a80355e4e46a5caaab7153
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7373
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

tvix/eval/src/vm.rs

@@ -694,7 +694,8 @@ impl<'o> VM<'o> {
                 let mut upvalues = Upvalues::with_capacity(blueprint.upvalue_count);
                 self.populate_upvalues(upvalue_count, &mut upvalues)?;
                 self.push(Value::Closure(Closure::new_with_upvalues(
-                    upvalues, blueprint,
+                    Rc::new(upvalues),
+                    blueprint,
                 )));
             }