BOLT-1132: Follow-up unit tests for Enphase grid-services historical backfill (PR #11725)

Artem (Slack 1780651334.371449) asked for an MR adding tests for the two files added by merged PR #11538. Sub-agent authored tests for gridServicesHistoricalCoordinator (createTimeChunks + coordinate) and enphaseGridServicesHistoricalSitePoll (addJob + processJob + mapJobToRecordPayload). Branch: artem-agent/bolt-1132-historical-backfill-tests. Local jest blocked by workspace symlink env-issue; eslint clean; relying on CI. Watching.