Add qiskit-experiments integration tests

Verify standard experiments run end-to-end: `StandardRB`, RB over packed/concatenated circuits, a failing job, cancellation, and metadata
round-trip.

Start by locating the existing integration-test setup and the entry points used to run standard experiments. Add coverage for StandardRB, packed and concatenated RB circuits, failing jobs, cancellation, and metadata round-trips; done means each listed scenario runs end-to-end and passes.

Written by the indexing model from the issue text.