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 string literal split with ~ ("a" ~ "b") is the single literal "ab",
the way long values and namespace URIs are wrapped across lines. The fold
applies wherever a string literal is read: value literals and the URIs of
namespace/datatypes/include/external declarations.
