Extract mpv/key to input

To separate the concern from `mpv`

test/input/input_test.gleam

@@ -1,7 +1,7 @@
 import gleam/list
 import gleeunit
 
-import mpv/key.{type Key, Char, csi, esc}
+import input/key.{type Key, Char, csi, esc}
 
 pub fn main() -> Nil {
   gleeunit.main()

test/mpv/control_test.gleam

@@ -1,9 +1,9 @@
 import gleam/list
 import gleeunit
 
+import input/key.{type Key, Char}
 import mpv/control.{type Control}
 import mpv/internal/control as control_internal
-import mpv/key.{type Key, Char}
 
 pub fn main() -> Nil {
   gleeunit.main()