wip

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/mpv/mpv.gleam

@@ -52,6 +52,12 @@ pub fn new(exit: Subject(Nil)) -> Result(Nil, String) {
             read_input(data, inject_input, tap_input)
           })
 
+          process.spawn(fn() {
+            let assert Ok(_) = process.register(process.self(), tap_input_name)
+
+            input_output_loop(tap_input)
+          })
+
           Ok(Nil)
         }
       }