feat(idempotency): postgres IdempotencyStore implementation

Joakim Olssonrequested to merge
feat/add-idempotency-support-tests into main

Implements eventsourced.IdempotencyStore (added in eventsourced v1.20.0) on the postgres event store:

  • CheckIdempotency: look up cached event by (idempotency_key, aggregate_type, aggregate_id), respects expires_at
  • StoreIdempotency: persists key + serialized event with TTL, ON CONFLICT DO NOTHING
  • CleanupExpiredIdempotencyKeys: removes expired records
  • New migration 20251101205358_add_idempotency.sql for command_idempotency table

Test plan:

  • CheckIdempotency: not-found / found / query error / unknown type / invalid JSON / non-pointer aggregate
  • StoreIdempotency: success / exec error / non-pointer aggregate / non-pointer event
  • CleanupExpiredIdempotencyKeys: success / no rows / error / RowsAffected error
  • reconstructIdempotentEvent: not reflect.Type / not Event branches
  • Coverage 99.5% (above main's 99.3%)

See pg/IDEMPOTENCY.md for usage.

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