decomposition of 4-body operator spin-free case

[DanielCalero1]

I wonder if you have worked on the implementation of the function "decomp_4op_to_2op_2rdm_sf", which in the original version of sqa says is not yet implemented.

I looked into your main branch and I saw that at least is not implemented there, but I wonder if you have worked in it somewhere else.

[ssh2]

No, we do not need the operator decomposition capabilities for our purposes, so we haven't work on this.