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

先阅读链接的 Discourse 讨论，然后在 CPython 的 asyncio 实现中定位 asyncio.run() 和 Runner 构造函数。确认针对 opt-in 参数 eager_tasks 约定的行为，并验证两个入口点都按指定方式接受并应用该参数。