Implement SFX for void enemy

[IDynamixI985]

• Audio Assets: Created the folder assets/third_party/sounds/void_enemy/ and added the audio files for idle, alert, chasing, caught, and defeated.

• Script (void_spreading_enemy.gd):

  • Added an exported dictionary state_sounds: Dictionary[State, AudioStream] to map each State directly to an AudioStream.
  • Updated _set_state to set void_sfx.stream = state_sounds[state] and trigger void_sfx.play().
  • Added await void_sfx.finished under State.DEFEATED to ensure the defeat audio finishes playing before proceeding.

• Animations: Updated the alert sound/keyframe in the VoidSpreadingEnemy animation.

• Audio for the void consuming tiles and props is still pending.

[IDynamixI985]

Hi, I've tried adding sound effects for the “void” enemy, but I can't really say if they go well with the background music, since I'm not very familiar with these sound-related issues. I look forward to your suggestions so I can improve what I've done.

[github-actions]

Play this branch at https://play.threadbare.game/branches/IDynamixI985/void_sfx/.

(This launches the game from the start, not directly at the change(s) in this pull request.)