test(tvix/eval): Add proptests covering trait impls for String

Add a suite of proptests covering the laws of the handwritten stdlib
trait impls (Eq, Ord, and Hash) for String, generated from a new set of
macros for generating those tests which can be applied to other types.

Change-Id: Ib3276c9e96fca497aece094e5612707d3dc77ccd
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6626
Autosubmit: grfn <grfn@gws.fyi>
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

tvix/eval/src/value/string.rs

@@ -177,3 +177,14 @@ impl Display for NixString {
         f.write_str("\"")
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::properties::{eq_laws, hash_laws, ord_laws};
+
+    eq_laws!(NixString);
+    hash_laws!(NixString);
+    ord_laws!(NixString);
+}