Environment

• Qiskit version: 2.0.0rc
• Python version: Any
• Operating system: Any

What is happening?

The implementations of DAGCircuit::__getstate__ and DAGCircuit::__setstate__ are missing logic to for stretch identifiers.

How can we reproduce the issue?

Pickling and unpickling a DAGCircuit with stretches should result in the stretches getting dropped.

What should happen?

The stretches should be preserved after unpickling.

Any suggestions?

No response