Tighter A* estimate on the orthogonal track, and --heuristic-weight

The grid search estimated the remaining distance as a straight line even
when only orthogonal steps exist; Manhattan is the tighter estimate those
moves admit and still never overestimates. --heuristic-weight W (default
1) makes it weighted A*: routes at most W times the shortest (tested).

src/freeroute/route/pipeline.py

@@ -150,6 +150,7 @@ def route_dsn_board_exact(
     dsn: DsnBoard,
     *,
     resolution: int = 1,
+    heuristic_weight: float = 1.0,
     edge_clearance_mm: float | None = None,
     layers: list[int] | None = None,
     max_passes: int = 10,
@@ -170,6 +171,7 @@ def route_dsn_board_exact(
     exact = route_board_exact(
         board,
         resolution=resolution,
+        heuristic_weight=heuristic_weight,
         via_half=_via_half_board(dsn, scale),
         edge_clearance=edge_clearance_board,
         trace_width=width_board,
@@ -187,6 +189,7 @@ def build_exact_routing_result(
     dsn: DsnBoard,
     *,
     resolution: int = 1,
+    heuristic_weight: float = 1.0,
     layers: list[int] | None = None,
     shove: bool = False,
     diagonal: bool = False,
@@ -204,6 +207,7 @@ def build_exact_routing_result(
         max_passes=max_passes,
         edge_clearance_mm=edge_clearance_mm,
         resolution=resolution,
+        heuristic_weight=heuristic_weight,
     )
     return _to_routing_result(exact.result, dsn, scale, layer_names)