feat(tvix/eval): Box Value::Catchable

This is now the only enum variant for Value that is larger than 8
bytes (it's 16 bytes), so boxing it (especially since it's not
perf-critical) allows us to get the Value size down to only 16 bytes!

Change-Id: I98598e2b762944448bef982e8ff7da6d6683c4aa
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10798
Tested-by: BuildkiteCI
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Autosubmit: aspen <root@gws.fyi>

tvix/eval/src/vm/macros.rs

@@ -44,7 +44,7 @@ macro_rules! cmp_op {
                     let span = generators::request_span(&co).await;
                     let ordering = a.nix_cmp_ordering(b, co, span).await?;
                     match ordering {
-                        Err(cek) => Ok(Value::Catchable(cek)),
+                        Err(cek) => Ok(Value::from(cek)),
                         Ok(ordering) => Ok(Value::Bool(cmp_op!(@order $op ordering))),
                     }
                 }