Migrate tests and console demo app to .NET 10

## Description

Now that .NET 10 is out, it's time to upgrade.

## Proposed solution

Migrate *VersOne.Epub.Test* and *VersOne.Epub.ConsoleDemo* projects and GitHub actions from .NET 9 to .NET 10.

## Additional context

.NET 10 announcement: https://devblogs.microsoft.com/dotnet/announcing-dotnet-10/