Returns the current rent arrear cycle of a leasing contract, which qualifies where the recovery
of an unpaid rent stands, together with the debt figures the cycle is measured against.

A cycle opens automatically when the tenant debt (unpaid_amount) exceeds the contract
threshold (unpaid_threshold_amount_in_cents) and closes when the debt is settled or a manager
closes it by hand. A contract may go through several successive cycles; this endpoint returns
the open one, or the most recent one when none is open.

rent_arrear is null when the contract has never entered an arrear cycle. A contract that is
unknown or belongs to another workspace returns a 404 instead.

This qualification is deliberately not embedded in the leasing contract payload: resolving the
cycle costs an extra query per contract, which the collection endpoint cannot afford.

This endpoint is read-only. Arrear statuses are driven by the platform (automatic detection and
reminder cycle) or updated by managers from the interface.