Grow the Tier-2 conformance corpus with 17 XSD regex cases through the
pattern-facet path: implicit whole-string anchoring, the character-class
escapes (backslash-d/w/s), Unicode category and negated-category escapes,
quantifier ranges (exact, bounded, open), alternation, grouping, negated
character classes, and class subtraction. All conform.
Part of #105 (Tier 2)
