Rip every user of a shared via, and judge vias round at the outline

Two connections of a net can share a via. The grid kept one owner per via
cell next to the claim list, and the search and rip-up read only that owner:
a route of another net through the via ripped the first user and left the
second's via under the new trace. The exact check then threw one of them
out. The search and rip-up now read the claim list, and the single owner is
gone.

The exact check also tested a via against the outline as its square box,
whose corner reaches past a 45-degree chamfer where the round via does not.
The grid keeps the via's centre its radius plus the edge clearance from the
outline, as KiCad measures it; the exact check now does the same.

kitspace_minisumo_v3 seed 4: 4 rejected connections to 0, 11 failed to 7.

tests/route/test_rollback.py

@@ -31,7 +31,7 @@ def test_occupancy_only_holds_routed_connections(name):
     router, _ = _routed_router(name)
     conns = router._conns
     assert all(conns[i].routed for i in router._cell_owner.values())
-    assert all(conns[i].routed for i in router._via_owner.values())
+    assert all(conns[i].routed for claims in router._via_claims.values() for i in claims)
     assert all(conns[i].routed for claims in router._halo.values() for i in claims)