### Description

The `sendRequest` method is asynchronous and notifies a 
`TransportResponseHandler` when it completes the excecution
(successfully or unsuccessfully). 

When opening the connection we only catch `NodeNotConnectedException`
( https://github.com/elastic/elasticsearch/blob/main/server/src/main/java/org/elasticsearch/transport/TransportService.java#L719 ) which is currently fine as no implementations
throw other type of exception however, it'd be best to catch `Exception` here
so the `handler` gets notified of potential exceptions (as opposed to the caller
having to `try/catch` the call to `sendRequest`)
test/framework/src/main/java/org/elasticsearch/transport/AbstractSimpleTransportTestCase.java
}
        };
        ConnectionProfile.Builder builder = new ConnectionProfile.Builder();
        builder.addConnections(
            1,
            TransportRequestOptions.Type.BULK,
            TransportRequestOptions.Type.PING,
            TransportRequestOptions.Type.RECOVERY,
            TransportRequestOptions.Type.REG,
            TransportRequestOptions.Type.STATE
        );
        try (Transport.Connection connection = openConnection(serviceB, serviceC.getLocalNode(), builder.build())) {
            serviceB.sendRequest(
                connection,
                "internal:action",
                new TestRequest("hello world"),
                TransportRequestOptions.EMPTY,
                transportResponseHandler
            );
            receivedLatch.await();
            serviceC.close();
            sendResponseLatch.countDown();
            responseLatch.await();
        }
    }
    public void testTransportStats() throws Exception {
        MockTransportService serviceC = buildService("TS_C", version0, Settings.EMPTY);
        CountDownLatch receivedLatch = new CountDownLatch(1);
        CountDownLatch sendResponseLatch = new CountDownLatch(1);
        serviceB.registerRequestHandler("internal:action", ThreadPool.Names.SAME, TestRequest::new, (request, channel, task) -> {