PyBEST: Improved functionality and enhanced performance

We present a methodological update to the Pythonic Black-box Electronic Structure Tool (PyBEST), a fully-fledged modern electronic structure software package. Among other things, these include the extensions to pair Coupled Cluster Doubles (pCCD) open-shell electronic structures via the ionization potential and double ionization potential equation of motion formalism (IP-EOM-pCCD and DIP-EOM-pCCD), tailored Coupled Cluster methods, EOM extensions on top of the linearized Coupled Cluster correction on top of pCCD, the configuration interaction correction on top of pCCD, and the static pCCD-in-DFT embedding. Furthermore, we have increased the performance of PyBEST by optimizing its underlying tensor contraction engine and providing GPU support via the CuPy library.