Add explosion stage 1 PNG assets for all directions

- Added BMP_1_EXPLOSION_DOWN.png to original and preview directories.
- Added BMP_1_EXPLOSION_LEFT.png to original and preview directories.
- Added BMP_1_EXPLOSION_RIGHT.png to original and preview directories.
- Added BMP_1_EXPLOSION_UP.png to original and preview directories.

These assets are part of the explosion animation for the game, enhancing visual effects during gameplay.

units/bomb.py

@@ -43,6 +43,9 @@ class Bomb(Unit):
         
         x_pos = self.position_before[0] * self.game.cell_size + (self.game.cell_size - image_size[0]) // 2 + partial_x
         y_pos = self.position_before[1] * self.game.cell_size + (self.game.cell_size - image_size[1]) // 2 + partial_y
+
+        if self.is_hidden_in_tunnel(image_size):
+            return
         
         self.game.render_engine.draw_image(x_pos, y_pos, image, anchor="nw", tag="unit")
 
@@ -131,6 +134,9 @@ class Explosion(Bomb):
         
         x_pos = self.position_before[0] * self.game.cell_size + (self.game.cell_size - image_size[0]) // 2 + partial_x
         y_pos = self.position_before[1] * self.game.cell_size + (self.game.cell_size - image_size[1]) // 2 + partial_y
+
+        if self.is_hidden_in_tunnel(image_size):
+            return
         
         self.game.render_engine.draw_image(x_pos, y_pos, image, anchor="nw", tag="unit")
 
@@ -186,4 +192,7 @@ class NuclearBomb(Unit):
         x_pos = self.position[0] * self.game.cell_size + (self.game.cell_size - image_size[0]) // 2
         y_pos = self.position[1] * self.game.cell_size + (self.game.cell_size - image_size[1]) // 2
 
+        if self.is_hidden_in_tunnel(image_size, position=self.position):
+            return
+
         self.game.render_engine.draw_image(x_pos, y_pos, image, anchor="nw", tag="unit")