iOS "Blaster" App: Press-and-Hold Emoji Projectiles

Problem

Build a minimal iOS app with a button fixed at the bottom. While the user presses and holds the button, the app emits emoji "projectiles" that travel upward at regular intervals until the press ends.

Requirements

1. Interaction
   • A bottom-aligned fire button.
   • Press-and-hold continuously fires projectiles at a fixed interval (e.g., every 80–150 ms).
2. Animation
   • Projectiles animate from the button area toward the top of the screen.
   • Choose and justify an approach: Core Animation, UIKit Dynamics, or SwiftUI.
3. Scheduling
   • Describe how you will schedule continuous firing while the button is held.
4. Cleanup
   • Either implement collision handling or ensure projectiles are cleaned up when off-screen.
5. Performance
   • Discuss performance considerations with many simultaneous projectiles and how to avoid jank.
6. Code Structure & Testability
   • Outline how you would structure the code for unit testing (e.g., timer abstraction, renderer abstraction, separation of UI and logic).

Assume a modern iOS target. You may use UIKit or SwiftUI; include brief code to illustrate your chosen approach and any key abstractions.