feat(tvix/eval): track whether locals needs to be finalised

When encountering a deferred local upvalue, the compiler will now mark
the corresponding local as needing a finaliser which makes it possible
to emit the OpFinalise instruction for this stack slot a little bit
down the line.

Change-Id: I3962066f10fc6c6e1472722b8bdb415a811e0740
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6338
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

tvix/eval/src/compiler/scope.rs

@@ -38,6 +38,10 @@ pub struct Local {
 
     // Is this local known to have been used at all?
     pub used: bool,
+
+    // Does this local need to be finalised after the enclosing scope
+    // is completely constructed?
+    pub needs_finaliser: bool,
 }
 
 impl Local {