I'm currently rewriting the blog plugin in Material for MkDocs (which is now free as part of the community edition), trying to improve interop with the plugin ecosystem, specifically plugins like awesome-pages or static-i18n. For this, I'm subclassing some of the existing classes. However, when we print nav for debugging, the names of the subclasses are not taken into account. This PR improves debug output when subclassing Page, Link or Section classes, which is especially useful for understanding navigation structure.

In this example, Archive and Category are subclasses of Page:

Section(title='Blog')
    Page(title=[blank], url='/blog/')
    Page(title=[blank], url='/blog/about/')
    Section(title='Archive')
        Archive(title='2023', url='/blog/archive/2023/')
        Archive(title='2022', url='/blog/archive/2022/')
    Section(title='Categories')
        Category(title='foo', url='/blog/category/foo/')
        Category(title='bar', url='/blog/category/bar/')