feat: window focus

[louis030195]

disclaimer: did only test on macos so need some testers

cargo run --example window

#171

need to update code for windows/linux

basically i check if the mouse is in the window

[louis030195]

seems is GetForegroundWindow ok

Retrieves a handle to the foreground window (the window with which the user is currently working). The system assigns a slightly higher priority to the thread that creates the foreground window than it does to other threads.

[nashaofu]

I accidentally merged the code, I opened a PR again #173