feat(wm): add active window border

This commit adds an optional active window border with a user-defined
colour. This is achieved by spawning a dedicated "border window" and
constantly placing it behind the focused window, or hiding it whenever
necessary.

Some constraints to note:

- The border will only be applied to windows managed by komorebi
- This means that if you temporarily float a window, it will lose the
  active window border
- There are some issues where parts of the border will be broken by
  applications like Zoom, even if Zoom is behind the currently focused
  window
- You probably want to turn off window shadows globally in Advanced
  System Settings -> Performance for the borders to have a consistent
  colour all the way around the window
- There is some inevitable jank due to trying to reposition both the
  focused window and the "border window" behind it simultaneously
- There are no borders for unfocused windows

resolve #182

Cargo.toml

@@ -4,5 +4,5 @@ members = [
     "derive-ahk",
     "komorebi",
     "komorebi-core",
-    "komorebic"
+    "komorebic",
 ]