refactor(auth): replace adapter Map with single adapter per station

refactor(auth): replace adapter Map with single adapter per station

Each charging station has exactly one OCPP version, making the
Map<OCPPVersion, OCPPAuthAdapter> unnecessary indirection. Simplify
to a single adapter field across the auth module.

- AuthComponentFactory: createAdapter() returns single OCPPAuthAdapter
- RemoteAuthStrategy: setAdapter()/clearAdapter() replace map ops
- CertificateAuthStrategy: readonly adapter field, no map
- OCPPAuthServiceImpl: single adapter, initializeAdapter() singular
- Tests updated to match new single-adapter API