feat: re-add class_commitment to pathfinder_getProof output

[CHr15F0x]

Fixes: #2489

I compared results between 15bdee2 and this branch and there's some differences:

• pathfinder_getProof serialized missing contract_data as null, now it's just skipped - I guess we should stick to the old behavior?
• contract_proof nodes were serialized in a slightly different way:

      {
        "binary": {
          "left": "0x5c0009baa6ae667d10ee6afc1c63550be043a58f975c03c846b7e841e90c2d8",
          "right": "0x3fda3c6bfc76ea5822fbac557957e40504996fad5396a5f9fe139d60acaa753"
        }
      },

as compared to

    "contract_proof": [
      {
        "left": "0x5c0009baa6ae667d10ee6afc1c63550be043a58f975c03c846b7e841e90c2d8",
        "right": "0x3fda3c6bfc76ea5822fbac557957e40504996fad5396a5f9fe139d60acaa753",
        "type": "binary"
      },

now.

Looking at the old code one would say that there's skip_serializing_none and the null-s should not appear in the output, but this is a bug, because the annotation must be put before the derive.

I think these differences should also be addressed. Wdyt?

[kkovaacs]

Yeah, sure, we shouldn't change how nodes are serialized in the response.

[CHr15F0x]

Yeah, sure, we shouldn't change how nodes are serialized in the response.

e7bc5cd

[kkovaacs]

LGTM