Add the Visual Subnet Calculator

[Joe-User]

What type of request is this?

New tool idea

Clear and concise description of the feature you are proposing

I use this all of the time. I think it would be great to see the Visual Subnet Calculator as a tool integrated into it-tools.

Is their example of this tool in the wild?

visualsubnetcalc.com
https://github.com/ckabalan/visualsubnetcalc

Additional context

No response

Validations

• Check the feature is not already implemented in the project.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.
• Check that the feature can be implemented in a client side only app (IT-Tools is client side only, no server).