performance: adaptive polling

[epic-64]

Introduce two FpsModes, Realtime and Performance.

• In Realtime mode, we run at 30 fps (this was previously the default)
• In Performance mode, we block until the next input (0 fps).

The game now always runs in performance mode, with one exception: an active puzzle is running and the remaining time is updated in real time.

So we can go from this:

To this:

The performance mode introduced numerous bugs that required adding several new flags, namely:

• BinaryNumbersGame.needs_render (to force render updated info in some cases where changes were not picked up in performance mode)
• BinaryNumbersPuzzle.skip_first_dt (to prevent game timer to skip ahead when the game was previously in performance mode - it would create giant dts)

[epic-64]

Forgot to enable squashing 😭