SwifterPM registry symlinks and static xcframework module maps handled correctly

SwifterPM registry mode now keeps each package root under .build/registry/downloads as a real directory whose top-level entries are symlinks into the SwifterPM cache, so Xcode’s dependency scanner sees the expected SwiftPM root shape. Local restores still avoid a recursive copy. For static xcframeworks that ship their own module.modulemap (CLibsql and similar), the static xcframework mapper now exposes a derived headers directory and the selected module map, instead of letting clang see two definitions of the same module.