--seed: shuffle the order connections are routed in

The router is deterministic, but its result depends heavily on which
connection routes first. A seed shuffles that order reproducibly, so a
change can be judged over several orders instead of the one it happened
to get.

src/freeroute/route/exact_router.py

@@ -94,6 +94,7 @@ def route_board_exact(
     edge_clearance: int | None = None,
     resolution: int = 1,
     heuristic_weight: float = 1.0,
+    seed: int | None = None,
 ) -> ExactRouteResult:
     """Route ``board`` orthogonally and verify the result with exact geometry.
 
@@ -122,6 +123,7 @@ def route_board_exact(
         edge_clearance=edge_clearance,
         resolution=resolution,
         heuristic_weight=heuristic_weight,
+        seed=seed,
     )
     edge = 0 if edge_clearance is None else edge_clearance
     outline = board.outline