Example outputs at double speed

When I run the demo tape:
```
# Where should we write the GIF?
Output demo.gif

# Set up a 1200x600 terminal with 46px font.
Set FontSize 46
Set Width 1200
Set Height 600

# Type a command in the terminal.
Type "echo 'Welcome to VHS!'"

# Pause for dramatic effect...
Sleep 500ms

# Run the command by pressing enter.
Enter

# Admire the output for a bit.
Sleep 5s
```

I get the following, which seems to be at 2x speed compared to the example in the README:

Start with the demo tape shown in the issue and compare its generated GIF with the example in the README, focusing on playback speed and the timing of Sleep and typing actions. Reproduce the discrepancy, trace the timing behavior from the CLI entry point, and consider the issue done when the demo output matches the README speed without breaking the stated delays.

Written by the indexing model from the issue text.