Refactor: encapsulate WebServerConfig fields and add constructor

[Rayato159]

This PR improves the encapsulation of WebServerConfig by making the ip and port fields private and exposing a clear constructor for external use.

🔨 Changes:

• ip and port are now private
• Added WebServerConfig::new(ip: IpAddr, port: u16) for construction
• Updated test to validate instantiation
• Maintains backward compatibility via Default implementation

Why ?

As discussed in Issue #4, public fields can lead to:

• Accidental external mutation
• Unclear API usage
• Reduced flexibility for future validation/extensions

This refactor helps establish a more robust and consistent API surface.

Releated Issue: #4

Let me know if you’d prefer accessor methods ip, port added as well, happy to include.

PS. This is tested screenshot, I have changed from default WebServerConfig from Addr: 127.0.0.1, Port: 8080 to Addr: 127.0.0.1, Port: 3000 and It's works.