Extract mpv/key to input

To separate the concern from `mpv`

src/mpv/control.gleam

@@ -2,8 +2,8 @@ import gleam/json
 import gleam/result
 import gleam/string
 
+import input/key.{type Key, Char}
 import mpv/internal/control as internal_control
-import mpv/key.{type Key, Char}
 import tcp/reason.{type Reason}
 import tcp/tcp.{type Socket}