Upsert leads in bulk

Create or update up to 100 leads in one call. Each lead is matched on email and written in its own transaction, so one invalid lead does not cancel the others. The team's lead limit is checked for each new lead using the current committed lead count. If an item would exceed that limit, earlier successful items remain saved and that item returns a leads_limit_reached error. If another request is creating leads for the team, the new lead's item returns status: failed with error lead_creation_in_progress and code 409. Retry only those failed items after one second; other items still run normally. The response is always 200: read status and errors of each result to know what happened to each lead. The call is free and consumes no request. When the person behind a lead has asked Hunter to delete their address, with a claim or a California DROP request, the lead is returned without it: email, confidence_score, verification.date and verification.status are null (HUN-23599).