Improve context manager

#### I'm submitting a ...
- [x] feature request

#### What is the current behavior?

Context manager for `allure.step()` does not allow assigning a variable name, which would be useful.

#### What is the expected behavior?

I'd like it if this worked:
```py
with allure.step('foo') as s:
print(s.title)
```

I expected that to work because this does work:
```py
s = allure.step('foo')
print(s.title)
```

#### What is the motivation / use case for changing the behavior?

Having this named context manager would keep very simple code DRY.

#### Please tell us about your environment:

- Allure version: 🤷‍♂️ I'm just doing the code review, not sure how to determine this.
- Test framework: pytest@^8.2.2
- Allure adaptor: allure-pytest@^2.13.5

Commencez par le point d’entrée du gestionnaire de contexte allure.step() et reproduisez les deux exemples d’utilisation avec pytest. La modification est terminée lorsque `with allure.step('foo') as s` expose la même valeur de `title` qu’une affectation directe ; ajoutez ou mettez à jour les tests pertinents concernant ce comportement.

Rédigé par le modèle d'indexation à partir du texte de l'issue.