Group @testable imports at the bottom, per public/rules-swift's swiftformat. A
behavior-preserving import-ordering reformat across 252 files (mostly tests).
--trailingclosures was deliberately not adopted (cosmetic, and swiftformat flags
it as caution-worthy).
Grow the Tier-2 conformance corpus with 7 Schematron cases (assert satisfied/
violated, an inert non-matching context, numeric comparison, and report fired/
not-fired) checked through the validation-driven harness. Moved to its own
suite (ConformanceSchematronTests) so the main corpus stays under the
type-body cap.
Part of #105 (Tier 2)
