Begin Tier-2 conformance checking, expressed through the OpenAPIKit validation
idiom rather than an ad-hoc loop. ConformanceCase is a Validatable named
expectation; Conformance.matchesExpected is a Validation<ConformanceCase, Void>
that emits one located ValidationError per diverging case, so a suite reports
every failure at once with the case name as its coding path. Seeded with a
Canonical XML 1.0 corpus (attribute ordering, empty-element expansion, comment
removal, CDATA-to-escaped-text, PIs, namespace rendering) and a test proving a
divergence is reported as a located failure. Growing the corpora against the
official suites is the ongoing Tier-2 work.
Part of #105 (Tier 2)
