Should BaseTCPStream.is_connection_dropped be async? #356

Looking at the urllib3 implementation of is_connection_dropped (https://github.com/urllib3/urllib3/blob/f7a4bed04085975918b3469bf94e195df9faf29a/src/urllib3/util/connection.py#L7-L26) it looks like their (pretty robust and battle tested 😄) implementation will sometimes block when testing if a connection is dropped (eventually calls into https://github.com/urllib3/urllib3/blob/f7a4bed04085975918b3469bf94e195df9faf29a/src/urllib3/util/wait.py#L105).

It looks like #346 was closed, deciding the current implementation is good enough for now with some great research, but it sounds like you may want to improve this API in the future in a way that might require blocking. Given you're pre-1.0 it would be good to get the APIs solid on what can eventually be async before 1.0 so you can more easily use a blocking implementation in the future.

I'm new here and just poking around so please LMK if there's any context I'm missing!