improve parent selection

benches/future_children.rs

@@ -8,9 +8,9 @@ use std::time::Duration;
 fn extend_layers_test(depth: usize) {
     let config = FutureMoveConfig {
         max_depth: depth,
-        start_pruning_at_minus: 4,
+        min_arena_depth_sub: 4,
         top_k_children: 2,
-        up_to_mod: 4,
+        up_to_minus: 4,
         max_arena_size: 10_000_000,
     };
     let mut fut = FutureMoves::new(Piece::Black, config);