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).
The namespace layer rejects malformed qualified names, declarations of
the xmlns prefix, misbindings of the xml prefix and either reserved
namespace name (including as the default namespace), and prefix
undeclaration; attributes must be distinct by expanded name; PI targets
and entity/notation names are NCNames; and DTD-typed xmlns values bind
their normalized form. Clears all 18 namespace cases from the eduni
baseline; xmltest valid/sa/012 joins the documented deviations per the
suite's own NAMESPACE='no' flag.
Closes#136
