Add ui module and ability to update its state

src/musicplayer.gleam

@@ -4,6 +4,7 @@ import musicplayer/input/input
 import musicplayer/input/key.{type Key}
 import musicplayer/mpv/mpv
 import musicplayer/musicplayer
+import musicplayer/ui/ui
 
 pub fn main() -> Nil {
   let input_keys_name: Name(Key) = process.new_name("input_keys")
@@ -15,13 +16,16 @@ pub fn main() -> Nil {
   // inject input
   let input_inject_name: Name(Key) = process.new_name("input_inject_keys")
 
+  // TODO should input.new just return the inject_subject?
   input.new(input_keys_name, input_stream_name, input_inject_name)
 
+  let assert Ok(ui) = ui.new()
   let assert Ok(mpv) = mpv.new()
 
   let exit = process.new_subject()
   let assert Ok(_) =
     musicplayer.new(
+      ui,
       mpv,
       input_keys_name,
       input_stream_name,