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).
Schematron tests, lets, and message expressions can now use key() backed
by xsl:key declarations parsed from the schema, document() loading an
external file through an injected documentLoader, and current() resolving
to the rule context node. A node-keyed function-table factory threads
through the evaluation. Completes the Schematron audit.
