feat(tvix/eval): implement list concatenation

Change-Id: Icdf715d116371a9f139bdf95266410bf967bef25
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6144
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

tvix/eval/src/vm.rs

@@ -151,6 +151,13 @@ impl VM {
                 }
 
                 OpCode::OpList(count) => self.run_list(count)?,
+
+                OpCode::OpConcat => {
+                    let rhs = self.pop().as_list()?;
+                    let lhs = self.pop().as_list()?;
+                    self.push(Value::List(lhs.concat(&rhs)))
+                }
+
                 OpCode::OpInterpolate(count) => self.run_interpolate(count)?,
             }