Add ability to listen (tap) the input

By doing something like
```
fn input_output_loop(input_output: Subject(List(String))) -> Nil {
  let output = process.receive_forever(input_output)

  echo output

  input_output_loop(input_output)
}
```

src/input/key.gleam

@@ -38,7 +38,9 @@ pub fn from_list(l: List(String)) -> Key {
     [ci] | [ci, _] if ci == input_introducer -> Continue(l)
     [ii, cmd, tail] if ii == input_introducer -> {
       case tail {
+        // Return
         "\r" -> Input(cmd)
+        // Backspace
         "\u{007F}" -> Continue([ii, string.drop_end(cmd, 1)])
         _ -> Continue([ii, cmd <> tail])
       }

src/mpv/control.gleam

@@ -10,8 +10,6 @@ import tcp/tcp.{type Socket}
 pub type Control {
   TogglePlayPause
 
-  Search
-
   Exit
 }
 
@@ -19,12 +17,7 @@ pub type ControlError {
   ControlError(details: String)
 }
 
-// TODO this should also have a context:
-// `/` in "artist list" "context will should be`control.Search`
-// `<some char>` in "create new playlist" context should be `control.Input`
-// `q` in most contexts should be `Exit`, but in a popup it should be `Close`
 pub fn from_key(key: Key) -> Result(Control, Nil) {
-  echo key
   case key {
     key.Char(char) -> char_control(char)
     _ -> Error(Nil)
@@ -35,7 +28,6 @@ fn char_control(char: String) -> Result(Control, Nil) {
   case char {
     " " -> Ok(TogglePlayPause)
     "q" -> Ok(Exit)
-    "/" -> Ok(Search)
     _ -> Error(Nil)
   }
 }

src/mpv/mpv.gleam

@@ -64,10 +64,6 @@ fn handle_message(
   control: Control,
 ) -> actor.Next(State(socket, inject, input_output, exit), Control) {
   case control {
-    control.Search -> {
-      process.send(state.inject_input, key.Continue([key.input_introducer]))
-      actor.continue(state)
-    }
     control.TogglePlayPause -> {
       echo "toggling play/pause"