Extract mpv/key to input

To separate the concern from `mpv`

src/mpv/mpv.gleam

@@ -4,8 +4,8 @@ import gleam/otp/actor
 import gleam/result
 import gleam/string
 
+import input/key
 import mpv/control.{type Control}
-import mpv/key
 import tcp/reason
 import tcp/tcp.{type Socket}