Visibility of nodes when using Virtualization

[nicolassargos]

Hi,

First, congratulations for your work, it's an amazing library!

I noticed an undesirable behaviour though when you use virtualization and change the visibility of nodes:

• I have enabled virtualization on nodes in the options.
• I have some nodes in my container and a switch for their visibility. When I hit the switch, the nodes disappear.
• When I pan, the nodes immediately reappear and I checked, their Visible property is set to true.

After checking your code, I think it comes from this line (https://github.com/Blazor-Diagrams/Blazor.Diagrams/blob/47e4c68d175f0c600c279383c2c77dce82205665/src/Blazor.Diagrams.Core/Behaviors/VirtualizationBehavior.cs#L60:
model.Visible = right > 0 && left < Diagram.Container!.Width && bottom > 0 && top < Diagram.Container.Height;

I guess you could have another property, like 'UserVisible' & 'VirtualizationVisible' and Visible could be => UserVisible && VirtualizationVisible.

In the meantime, I disabled virtualization as I'm still developping my own library on top of yours.

Thanks again for your work,
Nicolas.