BOLT-1275 additional-tests-v2: config + accumulation idempotency/boundary coverage

Artem requested v2 tests beyond #12252. Target: itron/config.ts (66 lines, currently 0 tests), common/config.ts (12 lines, currently 0 tests), plus accumulation idempotency + interval-boundary edge cases. Branch: artem-agent/bolt-1275-additional-tests-v2. Authorized via Slack thread 1781520916.636899 ts 1781608599.196749.