Speed up fidelity computation (#3926)
Speed up fidelity computation (#3926)

* speed up fidelity computation

* switch to schur

* lint

* revert all changes

* use default lapack driver for svd

Co-authored-by: Christopher J. Wood <70df86f979ffb183c2a587d1c81faf21b9e7777f@us.ibm.com>
QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py