Implement "idle" timeout for LazyConnection to close underlying connection when unused and automatically create new underlying connection on demand again

[clue]

By default, the createLazyConnection() method will now keep "idle" connection open for 60s and will
then end the underlying connection. The next request after an "idle"
connection ended will automatically create a new underlying connection.
This ensure you always get a "fresh" connection and as such should not be
confused with a "keepalive" or "heartbeat" mechanism, as this will not
actively try to probe the connection. You can explicitly pass a custom
idle timeout value in seconds (or use a negative number to not apply a
timeout) like this:

$factory->createLazyConnection('localhost?idle=0.1');

Builds on top of #87