Implement traps system: add Trap, Landmine, and EventHorizon classes with collision detection and interaction logic; integrate trap handling in the game scene and enemy AI.

game/traps/event_horizon.rb

@@ -0,0 +1,15 @@
+require_relative 'base'
+
+class EventHorizon < Trap
+  def initialize(x, y)
+    super(x, y)
+    @sprite = Gosu::Image.new("assets/images/event_horizon.png", retro: true)
+  end
+
+  def stepped_on(entity)
+    # this is not a weapon, so nothing
+    # it is instead destroyed after after being stepped on by enemy
+    $bus.emit(:stun, @x, @y)
+    entity == :enemy
+  end
+end