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 value of type QName compiles to its (namespace, local) pair via the
schema's xmlns/ns scope; the derivative engine threads the instance
element's in-scope bindings to value comparison in both the tree walk
and the streaming state (frames carry their bindings), so instance
prefixes and the default namespace resolve against the instance
document and unbound prefixes match nothing. Streaming also gains the
tree walk's empty-element rule. The spec suite's instance level is
fully clean: valid 289/289, invalid 291/291; only the asserted
schema-correctness class remains.
