The ported libyaml scanner and parser now serve every parsing path, so the
hand-rolled scanner, token cursor, and token event parser are dead. Removes
them and the old Token/NodeResult/NodeProperties types along with the unit
tests that exercised the old scanner directly. The remaining suite drives
the ported engine through the public API.
PureYAML now has a single parsing engine. 379 tests pass.
Add structured validation diagnostics, JSON and Yams comparison gates, and lazy token/event parsing so production behavior is measured without retaining full intermediate parser arrays.
