feat(tvix/vm): implement list construction

Change-Id: Iec2b4910800ab29daae6d71b58a8acd14ccb1cc1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6094
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>
Autosubmit: tazjin <tazjin@tvl.su>

tvix/eval/src/opcode.rs

@@ -32,4 +32,7 @@ pub enum OpCode {
 
     // Attribute sets
     OpAttrs(usize),
+
+    // Lists
+    OpList(usize),
 }