Set AsyncClient timeout None to send large data

[jeonghanjoo]

I'd already seen this issue https://github.com/healthjoy/async-firebase/issues/49

But to send large multiple messages at once, default httpx.AsyncClient timeout(5 seconds) is too short.

Usually sending 300 ~ 500 messages takes 5 ~ 10 seconds in my city(Seoul, Korea).

So since the httpx client cuts the connection after timeout, the whole request sometimes fails or responds as fail.

Just setting timeout None can make this timeout issue fixed.