Add eager_tasks parameter to asyncio Runner and run()

Feature or enhancement

Proposal:

We have an agreement that eager tasks should become defaults in asyncio eventually.

This issue implements the first step: it adds opt-in eager_tasks argument to run() function and Runner constructor.
Later we'll deprecate False value and enforce users to switch to eager tasks in their code.

See the linked discussion for details.

Has this already been discussed elsewhere?

I have already discussed this feature proposal on Discourse

Links to previous discussion of this feature:

https://discuss.python.org/t/make-asyncio-eager-task-factory-default/75164/10

Linked PRs

• gh-128293

Lisez d’abord la discussion Discourse liée, puis localisez asyncio.run() et le constructeur de Runner dans l’implémentation asyncio de CPython. Confirmez le comportement convenu pour l’argument opt-in eager_tasks et vérifiez que les deux points d’entrée l’acceptent et l’appliquent comme spécifié.