feat(tvix/eval): Implement builtins.sort

This is a bit tricky because the comparator can throw errors, so we
need to propagate them out if they exist and try to avoid sorting
forever by returning a reasonable ordering in this case (as
short-circuiting is not available).

Co-Authored-By: Vincent Ambo <tazjin@tvl.su>
Change-Id: Icae1d30f43ec1ae64b2ba51e73ee467605686792
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7072
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

tvix/eval/src/value/list.rs

@@ -1,5 +1,5 @@
 //! This module implements Nix lists.
-use std::ops::Deref;
+use std::ops::{Deref, DerefMut};
 
 use crate::errors::ErrorKind;
 use crate::vm::VM;
@@ -135,3 +135,9 @@ impl Deref for NixList {
         &self.0
     }
 }
+
+impl DerefMut for NixList {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}