Add a few seconds buffer time where all players are invincible when the game initially starts

[Srushtika]

Currently, the game logic is so that the ship starts at a random position and moves with random speed and direction. This means the players don't really have enough time just when the game starts to understand the ship's position and try to escape. It would be worth making all the player invincible for about 2 seconds so they don't die even if a bullet hits them in the first two seconds of gameplay.