[PATCH] Add defense timer

[nivivon]

👋 Hey! Thank you so much for making this efficiency tile trainer. I've been finding it super useful. As I was practicing defense, I realized that I was missing the urgency that comes from a trainer so I just ported over the one from the Trainer.

How I Tested

Switch to "folding" tab.

• When you already have the timer enabled, it immediately starts (with a 2 second bonus, just like trainer).
• If you don't, there's no timer visible. When you toggle it, it starts counting down.
• If you let the time run out on the first hand, it discards the last drawn tile.
• If you let the time run out on a subsequent hand, it discards the last drawn tile.
• If you disable the timer while it's running, it disappears and stops discarding tiles.
• When the hand is over, the timer stops running.
• When you click "New Hand" after, the timer resets to the settings values with the 2 second buffer.