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).
Ports parser.c: the one-event-at-a-time state machine that turns the
scanner's token stream into the YAML event stream. Covers stream and
document framing, directive processing with %TAG handle resolution and
default handles, the node property/tag/anchor production, block and
indentless sequences, block mappings, and flow sequences and mappings
including the single-pair `?` mapping forms.
Output verified against the libyaml reference event dumper: the empty
mapping value, %TAG resolution, and shorthand tags all match byte for
byte. 331 tests, no regression.
