refactor(auth): remove getAuthCache from interfaces, own cache in service

refactor(auth): remove getAuthCache from interfaces, own cache in service

Remove getAuthCache() from AuthStrategy and OCPPAuthService interfaces.
Store authCache directly as private field on OCPPAuthServiceImpl during
initializeStrategies(), eliminating indirect access through LocalAuthStrategy
for clearCache, invalidateCache, and updateCacheEntry operations.

Add getTestAuthCache() helper to MockFactories to encapsulate cache
access in tests. Harmonize all test files to use the shared helper
instead of ad-hoc cast chains. Fix broken OCPPAuthIntegrationTest
references and extract KNOWN_STRATEGIES constant.