Support (and provide tests and examples for) multithreading

Now that WASI-SDK 34 has been released with `wasm32-wasip3` support for pthreads via the Component Model's cooperative multithreading feature, we should be able to support multithreading in Python code. Alex Crichton has [run the CPython test suite with multithreading enabled](https://github.com/WebAssembly/wasi-libc/pull/850) with a few patches. In theory, things should "just work" once we apply those patches to the CPython fork we're using in this project.

Note that #242 is a prerequisite for this.

Commencez par examiner l’issue préalable #242, le fork de CPython utilisé par ce projet et les patches discutés dans wasi-libc PR #850. Activez la prise en charge de pthreads dans WASI-SDK 34, puis vérifiez la suite de tests de CPython et ajoutez les exemples et tests de multithreading demandés.

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