The iterator return from `aiofiles.os.scandir()` is blocking, may block event loop

[9-2-1]

aiofiles.os.scandir() is asynchronous while the returned iterator is not. Iterating the iterator may block asyncio event loop.

import time
import asyncio
import aiofiles
large_folder_in_slow_disk = "H:\photos"
use_list = True
async def main():
    entries_iter = await aiofiles.os.scandir()
    if use_list:
        print(f"start_time: {time.monotonic():>10.5f}")
        entries = list(entries_iter) # It's a Iterator, not AsyncIterator, may block while iterating
        print(f"end_time: {time.monotonic():>10.5f}")
        # during the time asyncio event loop may helt
    else:
        print(f"start_time: {time.monotonic():>10.5f}")
            for entry in entries_iter: # Not async
                print(f"iter: {time.monotonic():>10.5f}")
                # can notice that iterating consume time

[rodrigobnogueira]

I can confirm this issue from production usage over NFS: await aiofiles.os.scandir(...) itself is async, but iterating the returned iterator was still synchronous and could stall the event loop on slower network storage.

I opened a draft fix here: #226

The approach wraps the scandir iterator so async for advances entries via the executor (non-blocking), while preserving backward compatibility for existing synchronous iteration patterns.