qdjj_solver: QP and DMRG solvers for superconducting quantum impurities

qdjj_solver provides quasiparticle-expansion and density-matrix renormalization
group solvers for superconducting quantum-impurity models. It calculates low-
lying many-body energies, impurity charge and spin, Josephson currents, and
transition matrix elements. The repository includes Python interfaces, a native
C++ implementation for the quasiparticle solver, examples, validation tests,
and research applications.