Add retry() api to exercises

        this.#execute.bind(this.#context)()

    }

    /**

     * Allow the user to retry the exercise after they failed, reusing their

     * current terminal session etc.

     * 

     * This is accomplished by restarting the exercise in a context that

     * disables e.g. prepareWith, but normally allows awaiting manual confirmation.

     */

    retry() {

        this.#context = new ExerciseRetryExecutionContext(this.#context)

        this.start()

    }

    /**

     * Inform the execute function that the user has manually confirmed that

     * they are done with the exercise.

    }

}

/**

 * Exercise execution contexts for retry attempts. Disables

 * - describe()

 * - prepareWith()

 * - clear()

 */

class ExerciseRetryExecutionContext extends ExerciseExecutionContext {

    /**

     * Create a ExerciseRetryExecutionContext

     * @param {ExerciseExecutionContext} oldContext An old context from which handlers are inherited

     */

    constructor(oldContext) {

        super()

        this._describeHandler = oldContext._describeHandler

        this._verifyHandler = oldContext._verifyHandler

    }

    describe() {}

    async prepareWith() {}

    async clear() {}

}

/**

 * A test. It has a human-readable name and a list of exercises.

 */