3.0.0

Changed

• Builds and tests on Linux. Keychain has no Linux equivalent, so KeychainSecureStore is behind
  #if canImport(Security) and PersistenceKeychain becomes an empty module there rather than a
  build failure. SecureStore stays in PersistenceCore and remains available everywhere, so a
  Linux caller conforms their own type (libsecret, a KMS, an encrypted file) and injects it.