Connection Timeouts and Resetting State Attributes

In practice, connection instantiation can block indefinitely while waiting for an identify response and so we introduce a timeout here. This manifested in a couple of ways, but most stellarly, we encountered instances where all connections died and the connection checker was blocked on such a connection. This effectively kills the consumer while busy-waiting.

The second issue is that we weren't resetting all stateful variables in a connection when re-establishing a connection. Of particular note was `Connection._buffer`, the connection's read buffer. This meant that when re-establishing a connection, we'd sometimes have un-consumed responses from the server in the read buffer, which would get popped off before reading a legitimate identify response. In practice, it meant we misidentified servers as not supporting feature negotiation (`OK` responses were interpreted as identify responses).
`nested` is deprecated, but i don't know if you can use the normal `with` and comma syntax since you are flattening a list.