Consider repetitions in TB probing (#1027)

has_repeated was hardcoded to false, so Fathom never knew if the root
position had repeated before, and could rank a drawn position as a win.

Search usually catches this via upcoming_repetition and is_draw, but
when DTZ succeeds we stop probing TB in search. The wrong score then
gets written to TT and returned via TT cutoff before any repetition
check can correct it, which might cause the engine to report an
incorrect eval.

Bench: 2851948

Author: Saphereye

src/board.rs

@@ -260,6 +260,10 @@ impl Board {
         self.state.repetition != 0 && self.state.repetition < ply
     }
 
+    pub const fn is_repetition(&self) -> bool {
+        self.state.repetition != 0
+    }
+
     pub fn draw_by_fifty_move_rule(&self) -> bool {
         self.halfmove_clock() >= 100 && (!self.in_check() || self.has_legal_moves())
     }

src/tb.rs

@@ -117,7 +117,7 @@ pub fn rank_rootmoves(td: &mut ThreadData) {
             0,
             ep_square,
             td.board.side_to_move() == Color::White,
-            false,
+            td.board.is_repetition(),
             true,
             tb_ptr,
         );