Added support for connection viability updates

[Cartisim]

Enhancement: Integration of Viability Handler in Network.framework

We have successfully integrated the viabilityUpdateHandler from Network.framework into NIOTransportServices, enabling developers to leverage the full potential of the Network.framework API.

This enhancement provides adopters with critical insights into the viability of connections to remote endpoints. By being informed about the current network status, developers can implement a more responsive and adaptive approach to network behavior and conditions.

Modifications

• Introduced two new methods along with corresponding calls to these methods within the Network.framework handler.
• These handlers trigger the NIO InboundEventsTriggered method, allowing consumers to respond to network changes effectively.
• Developed two structs within NIOTSNetworkEvents to accompany the InboundEventsTriggered methods, ensuring seamless data transfer.
• Conformed these structs to Sendability for compatibility with the required operating systems.

Result

Clients can now receive viability events from Network.framework, enhancing their ability to manage network connections dynamically

[glbrntt]

Thanks for doing this, it seems like a useful addition.

Presumably we get a notification when a connection is established? If so it means we should be able to write a test that verifies we actually get the notification. Do you think you'd be able to add one? It looks like NIOTSEndToEndTests.swift would be a good place to start.

[glbrntt]

Left a couple of small comments but this looks great otherwise

[glbrntt]

This looks good to me, thank you! @Lukasa did you want to look as well?

[glbrntt]

@swift-server-bot test this please

[Lukasa]

Nice one, thanks @Cartisim!