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).
An xs:attribute declaration carrying a default value constraint was accepted
alongside use="required" or use="prohibited"; XSD 1.0 src-attribute.2 requires
use to be optional when default is present (a default makes the attribute
optional). The check rides the existing value-constraint walk, gated to
XSD-namespace attribute declarations reading the unprefixed default/use, and is
per declaration. Only fixed (not default) may pair with use="required".
XSTS: invalid schemas accepted 469 to 462, no other bucket raised. Disclosed
under-rejection: a whitespace-padded use=" required " (NMTOKEN actual value
"required") is not flagged.
