The reader treated every list paragraph as a new list item, so a list
item containing several paragraphs was split into one item per
paragraph. In the RTF list model a new item is marked by a
`{\listtext ...}` destination group; a list paragraph lacking one is a
continuation of the current item.
Track whether a `{\listtext}` group was seen (`sListText`) and, in
`emitBlocks`, append a continuation paragraph (no `\listtext`) to the
current item rather than starting a new one.
Adds a `list_multiparagraph` reader test.
Co-Authored-By: Claude <noreply@anthropic.com>
