The scalar event now carries the scanner token's end mark, so a located
scalar's range spans the whole token (end exclusive, one past the last
character) instead of being start-anchored. This gives consumers exact
highlight widths and is the prerequisite for surgical, position-based
text edits. Only the scalar event case gained a field; the value tree,
its equality, and the event dump (which compares value and style, not
marks) are unchanged, so the canonical-event and whole-suite gates stay
green (343 tests).