refactor(tests): add shared test helpers and fixtures for DRY compliance

refactor(tests): add shared test helpers and fixtures for DRY compliance

- Add timer helpers (withMockTimers, createTimerScope) in TestLifecycleHelpers.ts
- Add auth mock factories (createTestAuthConfig, createMockAuthCache, etc.) in MockFactories.ts
- Add transaction fixtures (IdTokenFixtures, TransactionContextFixtures) in OCPP20TestUtils.ts
- Add request tracking helper (createMockStationWithRequestTracking) for OCPP tests
- Refactor AuthStrategy tests to use shared factories (~490 LOC saved)
- Refactor TransactionEvent tests to use shared fixtures and helpers

14 files changed, 585 insertions(+), 752 deletions(-) = 167 net LOC saved