feat: disabled options

[gabrielchl]

summary:

• add disabled options (used in select and multi-select components)
• these options will be rendered (including the filtered list), but un-toggle-able
  • select: you can't select that option
  • multi-select: you can't toggle that option
• color-wise, they use the same color description does

(i'm not sure how the gif is best generated for the readme)

example usage:

huh.NewOption("Charm Sauce (sorry, we've run out!)", "Charm Sauce").Disabled(true),

example form question:

Toppings:
> [ ] Lettuce
  [ ] Tomatoes
  [ ] Charm Sauce (sorry, we've run out!)
  [ ] Nutella

example GIF:

closes #77