test(tvix/eval): Make proptests a bit smaller

Generate smaller recursive values for generated Values, and run fewer
cases for the attrs proptests which are particularly egregious.

Change-Id: Ia35c7c120270feaf045be1deb440c87ebb185c27
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6716
Autosubmit: grfn <grfn@gws.fyi>
Reviewed-by: tazjin <tazjin@tvl.su>
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

tvix/eval/src/value/arbitrary.rs

@@ -63,7 +63,7 @@ fn leaf_value() -> impl Strategy<Value = Value> {
 }
 
 fn non_internal_value() -> impl Strategy<Value = Value> {
-    leaf_value().prop_recursive(10, 256, 10, |inner| {
+    leaf_value().prop_recursive(3, 5, 5, |inner| {
         prop_oneof![
             any_with::<NixAttrs>((
                 Default::default(),