add upkeep method to AsyncSession

[kadamprashant1]

This change introduces the upkeep() asynchronous method to the AsyncSession class, bringing feature parity with the synchronous Session class and enhancing its capabilities for long-running applications.

[lexiforest]

Since there is no multi interface for upkeep. I guess this is the only way to send ping frames, I will have some style fixes and then merge. Thanks.

[kadamprashant1]

Thanks @lexiforest!

[Manouchehri]

Any progress on this?

[sarperavci]

I'd suggest this approach rather than processing handles concurrently. It's safer against pool starvation since each handle is returned immediately after upkeep and it can also be used as a standalone utility:

async def upkeep(session: curl_cffi.AsyncSession) -> list[int]:
    """
    Performs connection upkeep for all idle connections in the pool.
    """
    session._check_session_closed()
    
    results = []
    curls: List[curl_cffi.Curl] = []
    
    # Drain pool
    while True:
        try:
            curls.append(session.pool.get_nowait())
        except asyncio.QueueEmpty:
            break
    
    # Upkeep and return immediately
    for curl in curls:
        if curl:
            results.append(curl.upkeep())
        session.pool.put_nowait(curl)
    
    return results

Since curl.upkeep() just calls curl_easy_upkeep() (which is a quick C call to send PING frames), there's no need for run_in_executor.