Route with copper zones, and let vias into no-tracks areas

freeroute ignored the DSN's planes (KiCad's zones), so it never knew that
pads in a pour are joined by it. On the rc4 power stage those pads sit
inside "keep router off" areas as well, and every connection to them was
dropped without a word.

- Read (plane <net> <shape>) and put each zone on the board as a
  ConductionArea of its net. Zones are not obstacles: KiCad refills them
  around other nets' copper.
- The grid groups each net's pads and zone pieces that copper already
  joins (a pad in a zone, two zones sharing a pad) and routes only between
  groups. A connection may end on a zone by a via inside its copper, or by
  a track where tracks are allowed.
- wire_keepout now blocks traces only, as KiCad's "no tracks" rule area
  does; via_keepout only vias; keepout both, in the grid and in the exact
  verifier.

rc4 power stage, exact engine, resolution 2: 2 unconnected, down from 8
(FreeRouting JAR: 12), no DRC errors.

src/freeroute/route/exact_router.py

@@ -143,10 +143,16 @@ def route_board_exact(
     for obstacle in board.get_obstacle_areas():
         if obstacle.layer not in signal_layers:
             continue
+        blocks = (
+            "all" if obstacle.blocks_wires and obstacle.blocks_vias
+            else "wires" if obstacle.blocks_wires else "vias"
+        )
         for tile in obstacle.tiles:
             box = tile.bounding_box()
             if not box.is_empty():
-                tree.insert(TreeShape(next(owner), -1, frozenset({obstacle.layer}), box))
+                tree.insert(
+                    TreeShape(next(owner), -1, frozenset({obstacle.layer}), box, blocks=blocks)
+                )
 
     via_layers = frozenset(signal_layers)
     accepted: dict[int, _Accepted] = {}
@@ -155,9 +161,12 @@ def route_board_exact(
     # 25-pin supply net costs that one connection, not the whole net.
     for net_no, wires, vias in sorted(result.connections, key=lambda c: c[0]):
         boxes = _copper_boxes(wires, vias, half_width, via_layers, via_half)
+        wire_count = len(_copper_boxes(wires, [], half_width, via_layers, via_half))
         if any(
-            tree.clearance_conflict(box, net_no, layer, clearance)
-            for box, box_layers in boxes
+            tree.clearance_conflict(
+                box, net_no, layer, clearance, "wire" if i < wire_count else "via"
+            )
+            for i, (box, box_layers) in enumerate(boxes)
             for layer in box_layers
         ) or (outline is not None and not all(outline.box_clear(b, edge) for b, _ in boxes)):
             continue  # exact-clearance conflict -> drop (may be recovered by shove)