feat: Add ConnectionReady event for connection state monitoring

[connorjamessmith]

Is your feature request related to a problem? Please describe.
I need to track when Lavalink nodes connect/reconnect for health monitoring in my Discord bot. Currently, there's a ConnectionClosed event but no corresponding ConnectionReady event for when connections are established.

Describe the solution you'd like
Add a ConnectionReady event to IAudioService that fires when a Lavalink node connection is established (both initial connection and reconnection).

_lavalinkClient.ConnectionReady += (sender, args) => {
    Status = HealthStatus.Healthy;
};

Describe alternatives you've considered

• Log parsing - Current workaround.
• Periodic connection checks - No suitable property exposed, less efficient than events

Additional context
I have a working implementation with tests ready to submit as a PR if this aligns with the library's direction.
Implementation: https://github.com/connorjamessmith/Lavalink4NET/tree/feature/connorjamessmith/connection-ready-event

[angelobreuer]

I added the Connectionready event here: #241
Does that fit your needs?

Ah, completely overlooked the "Additional context" part

[angelobreuer]

Your changes look good, if you want to create a PR, go ahead. We can then merge your changes to add the event

[angelobreuer]

Live on 4.2.0