test(charging-station): add Heartbeat/Ping and Error Recovery tests

test(charging-station): add Heartbeat/Ping and Error Recovery tests

Implement Wave 3 advanced tests covering timing intervals and error handling.

Heartbeat/Ping Intervals (13 tests):
- Add heartbeat start/stop/restart tests
- Add WebSocket ping interval tests
- Add meter values interval tests
- Add OCPP 2.0 transaction update interval tests
- Use timer mocking for fast execution

Error Recovery/Resilience (13 tests):
- Add reconnection logic tests with exponential backoff
- Add error handling tests for invalid messages
- Add graceful degradation tests
- Add cleanup verification tests
- All error scenarios handled without crashes

Total: 26 new tests (243 tests total)
All tests pass in 2.9s.