Improve JATS parsing with nested lists, inline formulas, ordered lists, content layers

[ceberam]

Requested feature

To catch up with the latest docling and docling-core developments, we should add the following features in the JATS XML parser backend:

• [ ] parse nested lists (currently only level 1 is addressed)
• [ ] add inline formulas in inline groups
• [ ] parse ordered lists (currently they are parsed as unordered lists)
• [ ] distribute content in body or furniture content layers
• [ ] support formatted text (bold, italic, underline, superscript,...)