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).
Ship the OpenAPIKit-style validation layer (builtin rules, warnings channel,
Validator tiers, coverage gates) and wire XSD compile checks through it. Advance
#161 with chameleon include validation, multi-container reference resolution,
and include targetNamespace composition rules so merged schema sets compile
correctly when a schemaLoader is provided.
A strict or lax wildcard must resolve elements declared in schema documents an
instance points at through xsi:schemaLocation, which the main schema need not
import. validate(_:schemaLoader:) now reads the instance's xsi:schemaLocation
and xsi:noNamespaceSchemaLocation hints, loads and compiles each referenced
document through the loader, and merges its global declarations in (the primary
schema wins on conflict). The plain validate(_:) is unchanged; the XSTS runner
resolves hints relative to the instance file.
XSTS: valid instances rejected 308 to 288 (the particle clusters whose
wildcard-matched elements live in a separate, instance-referenced schema).
Baseline updated; regression tests cover cross-document resolution, the loaded
type being enforced, and strict failure without the loader.
Refs #147, #129.
