Adding a test package to simplify testing interactive commands

[survivorbat]

Is your feature request related to a problem? Please describe.

It is not, but unit-testing huh required some work when I was building it into our CLI. I wrote an 'answering machine' that supplies the input stream of huh inputs based on the output

Describe the solution you'd like

I'd love to write a test package that provides the user with 2 streams to give to huh's WithInput and WithOutput methods, with settings to respond to certain inputs. Maybe something like:

package main

import "github.com/charmbracelet/huh/huhtest"

func TestHuhForm_DoesWhatItIsSupposedToDo(t *testing.T) {
  var formIn io.PipeReader
  var formOut io.PipeWriter
  var close func()

  formIn, formOut, close = huhtest.NewAnsweringMachine().
    AddResponse("How Are You Feeling?", "Amazing Thanks!").
    AddResponse("Would you like a drink?", huhtest.ConfirmNegative).
    Times(2).
    AddResponse("Please pick all options that apply", []string{"a", "b", "c"}).
    Once().
    AddResponses("Are you OK? (gonna ask you twice)", []string{"yes", "yes for sure"}).
    Start()

  // Alternative available: SetResponses(map[string][]string)

  defer formIn.Close()
  defer formOut.Close()
  defer close()

 // Act
 err := myForm.WithInput(formIn).WithOutput(formOut).Run()

 // Assert
 // [...]
}

Describe alternatives you've considered

Turning it into a separate library instead of incorporating it as a contribution here, which I'm fine with as well

Additional context

I'm asking it to see if this is the direction that you might be interested in exploring and what your thoughts are on such a framework