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 scanner records declaration provenance (internal-subset entities,
element models, attribute lists); the validator reports the three
standalone='yes' dependencies on the external subset: a default that
would be supplied, a non-CDATA normalization that would change a value,
and whitespace in externally-declared element content. The parser hides
externally-declared entities from standalone documents, so referencing
one reports as undeclared (WFC: Entity Declared, 2.9). The Sun section
is fully clean: not-wf 56/56, valid 28/28, invalid 74/74, no baseline.
Closes#134Closes#124
