[feat] Hyperkey support

[unsecretised]

I think hyperkey would be a nice touch to add to rustcast,

I think its simply adding a global listener, and then return nill, followed by doing a new CGEventTap which is just a bunch of modifiers.

Quoting chatgpt:

User holds your chosen key (say Caps Lock or F18).
Your app sets hyperDown = true and swallows the physical key event.
When user presses K while hyperDown, your app swallows that K event and posts a synthetic K with modifier flags control|option|shift command.
Result: other apps receive ⌃⌥⇧⌘K.