OVRTX sensor capture

Use the public client in addon/ and its tests. Sensor identity is the USD product path, not a Blender object name or output filename.

1. Run the focused tests/test_ovrtx_runtime_client.py and tests/test_ovrtx_session.py controls, then inspect a compatible native probe under scripts/ before adapting it.
2. Supply an explicit fixture, worker, native-client path, sensor paths, matching RenderVar paths, dimensions, time, and caller-owned output JSON.
3. Require successful worker start, simulation creation with every requested sensor, one bounded sample step, exact per-RenderVar reads, decoded frames, finite dimensions/data, deletion, and shutdown.
4. Run test_ovrtx_runtime_client.py and test_ovrtx_session.py; retain tests for deduplication, changed-sensor session identity, selected-product routing, iterator pages, and terminal errors.