Add shove-in-rooms and gate-placement fixtures and tests

rooms_shove_channel is the headline density win: a sealed NET_A wall
leaves no top<->bottom door, so plain room routing drops NET_C; with
shove=True NET_A is nudged aside and both nets route, DRC-clean and
deterministic. rooms_wide_door seats two nets through one wide gap at
distinct projected gate points with no shove.

Cover the occupancy-aware projection math directly, assert the four
foundation fixtures stay byte-identical under shove=True (shoves==0), and
extend the room DRC-clean parametrize with both new fixtures.

tests/route/test_room_router.py

@@ -26,6 +26,8 @@ SIMPLE = FIXTURES / "simple_2net.dsn"
 CROSSING = FIXTURES / "crossing_2net.dsn"
 KICAD = FIXTURES / "kicad_routable.dsn"
 NARROW = FIXTURES / "narrow_channel.dsn"
+SHOVE_CHANNEL = FIXTURES / "rooms_shove_channel.dsn"
+WIDE_DOOR = FIXTURES / "rooms_wide_door.dsn"
 
 
 def _clearance(dsn, scale):
@@ -37,7 +39,7 @@ def _clearance(dsn, scale):
 # --- DRC-clean invariant (same non-negotiable as the exact track) -----------
 
 
-@pytest.mark.parametrize("fixture", [SIMPLE, CROSSING, KICAD, NARROW])
+@pytest.mark.parametrize("fixture", [SIMPLE, CROSSING, KICAD, NARROW, SHOVE_CHANNEL, WIDE_DOOR])
 def test_room_router_output_is_drc_clean(fixture):
     dsn = parse_dsn(fixture.read_text())
     rooms, scale, _ = route_dsn_board_rooms(dsn)