fix(output): reuse termenv output (#715)

If the passed io.Writer is a termenv.Output, use it instead of creating
a new termenv.Output.

options.go

@@ -28,9 +28,13 @@ func WithContext(ctx context.Context) ProgramOption {
 // won't need to use this.
 func WithOutput(output io.Writer) ProgramOption {
 	return func(p *Program) {
+		if o, ok := output.(*termenv.Output); ok {
+			p.output = o
+		} else {
 			p.output = termenv.NewOutput(output, termenv.WithColorCache(true))
 		}
 	}
+}
 
 // WithInput sets the input which, by default, is stdin. In most cases you
 // won't need to use this.