Liveness check

[thelonelyvulpes]

This change introduces a liveness check timeout.

• Liveness checks will be completed when borrowing a pooled connection, given that the connection has been idle longer than the timeout.
• The driver, by default, will not add liveness checks, but this can be configured with WithConnectionLivenessCheckTimeout on the ConfigBuilder.

using var driver = GraphDatabase.Driver(uri, creds, 
    cb => cb.WithConnectionLivenessCheckTimeout(TimeSpan.FromSeconds(30));

Using a timeout of 0, all connections will complete a liveness check when taken from the pool; this ensures connections are healthy but comes at the cost of performance when running queries or starting transactions.