Written books lose their title and pages: the reader ignores {raw: ...} filterable text

What happens

Written books loaded from a world open empty: no title and no pages. A book that ships in a map chest, for example "A Partner" by Dylan Collins, shows nothing at all.

Why

A written book stores its content as filterable text, where a value can be a plain string or an object with a raw field:

minecraft:written_book_content = {
  title: {raw: 'A Partner'},
  author: 'Dylan Collins',
  pages: [{raw: "I'm glad you got here..."}]
}

WrittenBookContentImpl::read_data in crates/pumpkin-data/src/data_component_impl/book.rs only accepts plain strings: the title through c.get_string("title") and each page only when it is NbtTag::String. The {raw: ...} objects are ignored, so the title and every page are dropped when the item loads.

The writable book reader in the same file already accepts both shapes, so the two readers disagree with each other.

Also

Both write_data implementations store plain strings, but vanilla writes filterable text. A book signed on the server is serialized in a shape the client and other servers do not expect.

Steps

1. Load a world that has a written book in a chest, or give yourself one with pages.
2. Open the book: no title and no pages.

Expected

The title and pages load, and books the server writes keep the vanilla shape.