Move Core Data tests out of the Library package so that we can still use
the more efficient `swift test` for most tests.
Create a PassepartoutTests target only for tests that require
`xcodebuild`, like Core Data tests.
Eventually:
- PRs only run SwiftPM tests
- Releases run ALL tests with `scan` before `gym`
- Drop CocoaPods completely
- Make PassepartoutCore a Swift package
- Enable Bitcode to fix OpenSSL linkage (iOS)
- Update CI scripts without CocoaPods
Davide