gen_code - Create a CSS code out of two Tanner codes ๐แถป and ๐หฃ, each constructed out of two related graphs ๐ขโโก, ๐ขโโก, the graphs build out of a Cayley complex, which itself was based on a group G=SLโqโฑ and two generator sets A and B. For consistency of indexing of "qubits" โ "graph edges" โ "squares" and "local bits" โ "generator pairs" we have the edge_*_idx maps.