feat(技能图标): 添加技能冷却显示功能

- 新增 SkillIcon.gd 脚本用于管理武器技能图标显示
- 修改 CooldownProgress.gdshader 增加背景透明度参数
- 更新 CooldownTimer.gd 添加时间计算方法
- 重构 SkillIconBase.tscn 场景以支持新功能

scripts/Statemachine/CooldownTimer.gd

@@ -4,9 +4,11 @@ var cooldown: float = 100
 var lastStart: int = 0
 
 func isCooldowned():
-	return WorldManager.getTime() - lastStart >= cooldown
+	return timeSinceLastStart() >= cooldown
 func start():
 	var state = isCooldowned()
 	if state:
 		lastStart = WorldManager.getTime()
 	return state
+func timeSinceLastStart():
+	return WorldManager.getTime() - lastStart

scripts/Statemachine/SkillIcon.gd

@@ -0,0 +1,10 @@
+extends PanelContainer
+
+@export var weapon: Weapon = null;
+
+@onready var textureRect = $"%texture"
+
+func _physics_process(_delta):
+	if is_instance_valid(weapon):
+		textureRect.texture = weapon.avatarTexture
+		textureRect.material.set_shader_parameter("progress", clamp(weapon.cooldownTimer.timeSinceLastStart() / weapon.cooldownTimer.cooldown, 0, 1))