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

Lies zuerst die verlinkte Discourse-Diskussion, suche dann asyncio.run() und den Runner-Konstruktor in der asyncio-Implementierung von CPython. Bestätige das vereinbarte Verhalten für das opt-in-Argument eager_tasks und überprüfe, dass beide Einstiegspunkte es wie spezifiziert akzeptieren und anwenden.