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.
Add RelaxNG.validate(streaming:), driving the Brzozowski derivative directly
from the parse-event stream (the libxml2 xmlTextReader model). The derivative
is already incremental: the after-threaded pattern chain is the validation
stack, so only the residual pattern and a light per-element frame (for the
childrenDeriv ignorable-whitespace rule) are retained, never the tree. A
differential test asserts streaming agrees with the trusted tree engine across
valid, invalid, whitespace, and mixed-content documents. XSD streaming remains.
Part of #107, #105
