gh-140355: Simplify asyncio REPL code by removing threading and future handling

[frostming]

Signed-off-by: Frost Ming me@frostming.com

Linked issue:

• Consider removing the thread and future handling in asyncio REPL #140355

It fixes the following issues:

• python -m asyncio and breakpoint() will fovever error loop and mess up the terminal #138827
• mac: BASIC_REPL asyncio then ctrl+c will break the readline on mac #140163

There are also some minor user-facing changes:

• When an exception is raised, the traceback is more simple, with fewer frames
• Tasks created by asyncio.create_task() are not driven in the background, they will only be stepped in the next evaluation.