Add CLI to regenerate LibXC registry

[EBB2675]

it was briefly discussed in #237 with @ladinesa

a small CLI utility to (re)generate utils/libxc/data/registry.json using LibXC’s get_functional_info.py parser.

something like:

• Try importing get_functional_info directly

• Strip unused fields from the produced JSON.

• Write the filtered registry to the correct location (?)