Use anyio instead of asyncio

1. gather

Example：

import anyio


async def gather(*coros):
    results = [None] * len(coros)

    async def runner(coro, i):
        results[i] = await coro

    async with anyio.create_task_group() as tg:
        for i, coro in enumerate(coros):
            tg.start_soon(runner, coro, i)
    return results


async def foo(i):
    print(i)


async def main():
    await gather(*[foo(i) for i in range(5)])


if __name__ == "__main__":
    anyio.run(main)

2. run_until_complete

asyncio：

import asyncio
from typing import Coroutine
from tortoise import Toirtoise

def run_async(coro: Coroutine) -> None:
    loop = asyncio.get_event_loop()
    try:
        loop.run_until_complete(coro)
    finally:
        loop.run_until_complete(Tortoise.close_connections())

--> anyio:

import anyio
from typing import Coroutine
from tortoise import Toirtoise


def run_async(coro: Coroutine) -> None:
    async def runner():
        try:
            await coro
        finally:
            await Tortoise.close_connections()
    
    anyio.run(runner)