avoid mixing pure python and C implementation of asyncio

[kumaraditya303]

Currently writing tests in asyncio is difficult because we have two separate implementations. The C implementation overrides the pure Python implementation at runtime as such testing python implementation is tricky. I propose that the pure python implementation should use the pure python versions of things like register_task and enter_task so that the it gets tested properly and it makes debugging easier. There should not really be a case where we mix both the implementations, both should be separate.

Linked PRs

• gh-129874: avoid mixing pure python and C implementation of asyncio #129875
• gh-129874: improve asyncio tests to use correct internal functions  #129887
• gh-129874: improve test_tasks in asyncio to use correct internal functions #129890
• gh-129874: improve test_events to use correct task implementation #129891
• gh-129874: avoid mixing pure python and C impl in eager execution #130515
• gh-129874: improve tests to use correct implementations in asyncio  #130516