Due to discussion from #2542 and following work from closed PR #2568
This change refactors the external semaphore tests by unifying
`external_semaphores_import_export_fd` with
`external_semaphores_cross_context` tests, removing duplicated logic and
avoiding OS-specific conditions. The updated test now covers all
import/export handle types consistently across single- and multi-context
scenarios.
67fbbe4ee2