- A blank run at EOF now breaks the list without consuming the blank,
matching real marked: '- item\n\n' lexes as a tight list plus a space
token instead of a loose list whose raw includes the blank.
- Completes the 17.2.10 mid-document fix; same-marker continuation and
indented item content across blanks are unaffected.
- Added list/blank boundary token-shape tests (verified against marked
v15) since the tui incremental tests compare the lexer to itself.