Added the flying attribute to the drill weapon, unlocked on level 5.

This update brings:

1. Drill Weapon Modification:
- In response to player feedback that the Drill weapon was too weak, we have made the following changes:
- The Drill weapon is now unlocked at level 5 and renamed Jet Driller.
- Hold down the left mouse button to activate the drill, and press the jump button to enter Flight Mode. In Flight Mode, players can reach previously inaccessible areas and engage bosses in the air.
- Press and hold the left mouse button to store energy. When the energy is fully stored, releasing the button will cancel Flight Mode and fire a drill armor-piercing bullet.
- Due to its large size, the drill weapon can also act as a shield to block some enemy bullets.

2. Weapon Replacement:
- The default Knife and Pistol can now be directly replaced with a better melee weapon or pistol, without taking up additional item slots.

3. UI Adjustment:
- You can now use shortcut keys 1-6 to switch weapons directly, and the game UI will update accordingly.