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).
A top-level xs:element declaration (a direct child of schema, or of redefine) was
accepted with ref, form, minOccurs, or maxOccurs. A global element is a
declaration, never a particle or a reference, so those local-use attributes are
prohibited by the schema-for-schemas topLevelElement. The top-level-attribute
applicability scan is generalized into topLevelDeclarationErrors, driven by a
per-kind forbidden-attribute map, covering both attribute and element. A local
element particle inside a content model is unaffected.
XSTS: invalid schemas accepted 424 to 422, no other bucket raised.
