test: use shared constants and enums instead of hardcoded literals (#2040)

test: use shared constants and enums instead of hardcoded literals (#2040)

Replace hardcoded literals in recent tests with the shared constants/enums they duplicate (single source of truth, no behavior change; values are byte-equivalent):

- OCPP20 PostStopResurrection: GenericStatus.Accepted / ReportBaseEnumType.FullInventory instead of raw 'Accepted' / 'FullInventory'
- OCPP20 RequestStartTransaction: OCPP20ChargingRateUnitEnumType.A instead of 'A' as OCPP20ChargingRateUnitEnumType casts
- OCPP16 SmartCharging: TEST_ONE_HOUR_SECONDS instead of the 3600 duration literal
- UIHttpServer: ProcedureName.* instead of raw procedure-name strings
- Remove the now-unused TEST_PROCEDURES test constant (ProcedureName is the canonical source)