Implement timeout support for Connection.isValid(int)

[mrotteveel]

When Connection.isValid(int) was implemented in #176, it was implemented without timeout support. At some point, we also implemented registering a warning when a non-zero value was supplied. This is not an optimal solution (e.g. see this).

Although timeouts aren't possible with native/embedded, we could support it for pure-java with temporarily changing the blocking read timeout, and for native/embedded we could maybe use a CompletableFuture or something.

[mrotteveel]

Implemented.

For Jaybird 4.0.6, the timeout is used as a network timeout. This only works for pure Java connections. In addition, for Jaybird 5, the check is performed asynchronously, using the timeout as the deadline of the async check, which makes the timeout also applicable to native connections.