Ability to generate DF block encoding without performing JW

[max-radin]

@KaterinaGratsea and I found that generating the double factorized block encoding for large instances requires a lot of memory because the init method of ChemicalHamiltonian will perform a Jordan-Wigner transform on the Hamiltonian. For example, it was not possible to generate the block encoding for a 46 orbital Hamiltonian on a machine with 30 gb of memory.

Since the JW transformed Hamiltonian is not needed for the DF block encoding, I think it would be good to update ChemicalHamiltonian to not perform JW during initialization. Note however that this is not a blocker for us: we're able to work around the issue by just commenting out these lines.

[kjm538]

Thanks for bringing this up. This has been fixed in v1.2.0 which is now available.