turret upgrades

allow player to upgrade turrets to deal more damage, slower cooldown times, fire more bullets, ect

a side menu popup when the player is on the turret?

Start by locating the turret implementation and the player-to-turret interaction or UI entry point. Define how upgrades should affect damage, cooldown, and bullet count, and decide how the side menu is opened and presented. Done means the upgrade flow and all requested turret effects work consistently in the game, but the issue does not specify tests or acceptance details.

Written by the indexing model from the issue text.