Adds an opt-in harness that runs PureYAML over the canonical YAML 1.2
corpus (github.com/yaml/yaml-test-suite) and reports a parse-level pass
rate: a should-parse case must parse, a should-error case must be
rejected. The data is fetched into a gitignored location by
scripts/fetch-yaml-test-suite.sh, never vendored, and the run is gated
behind PUREYAML_RUN_YAML_TEST_SUITE=1 so the default suite is unaffected.
This turns 'best YAML library' from an assertion into a tracked number.
Baseline: 211/333 (63.4%) parse-level: 177/255 valid documents parse,
34/78 invalid documents are rejected. So 78 valid docs are not yet parsed
and 44 invalid docs are wrongly accepted. The stricter value-level check
against each case's in.json is the next step.
Mihaela M
9298536e52