deltachat-rpc-client: get rid of asyncio

[link2xt]

asyncio seems to be a bad choice for new Python bindings. There are several reasons for this. It requires users to learn how to start asyncio loop in their application. Code is full of async and await keywords, which simply add noise, most of the changes in this PR are the result of mechanical removal of these keywords. Garbage-collected tasks are automatically cancelled, unlike threads, which is a well-known footgun but is unavoidable for new asyncio users. pytest-asyncio is not compatible with pytest-xdist, making it impossible to run tests in parallel. There are subtle differences to the rest of the standard library for I/O, recent issue #4782 actually broke faqbot because readline() in asyncio fails on too long lines. With the upcoming GIL removal in Python 3.12 and following versions, I expect more asyncio packages to break, at the moment aiohttp is broken and I had to revert CI to 3.11 in #4776.

This change replaces asyncio with threading and enables pytest-xdist for deltachat-rpc-client. Most of the changes are in the reworked rpc.py and adapting the tests. The rest is the removal of async and await.

For most bots migration to new API is as simple as removing asyncio loop and all await keywords before Delta Chat API calls. For bots using asyncio libraries, they can keep asyncio loop and call now blocking functions with asyncio.to_thread from async functions.

[adbenitez]

maybe now I can try to port simplebot to the new bindings :)

[link2xt]

maybe now I can try to port simplebot to the new bindings :)

First step would be porting existing https://github.com/deltachat-bot/faqbot and its dependency https://github.com/deltachat-bot/deltabot-cli-py I thought.

[link2xt]

I have updated this bot: https://github.com/deltachat/pingpong
deltachat/pingpong@bd1283a