Fails to unmarshal transaction types with keyless signature

[conorpp]

The current Signature type found in Transaction currently handles signatures that look like this:

      "signature": {
        "sender": {
          "public_key": "0xd2b2e1e78128ba9482232adafb90b6adfa710c3d8b82510423af5eb6a16b3bca",
          "signature": "0x0e8491dda3ff0925ba227631e33438d95a01da6529e3bc83f3d11de4b97995b2d39f47b2d9b6321a0097f6eb7b62f017e0056324d5e49f2270f15cb354a0b90c",
          "type": "ed25519_signature"
        }

However, there are transaction signatures that look like:

      "signature": {
        "sender": {
          "public_key": {
            "value": "0x1b68747470733a2f2f6163636f756e74732e676f6f676c652e636f6d2076fb5829c1cbd6541428a652a49595cdeaeb0cc5505bfed698563c1f7b53d72f",
            "type": "keyless"
          },
          "signature": {
            "value": "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",
            "type": "keyless"
          },
          "type": "single_key_signature"
        }

Example: https://aptoscan.com/transaction/2374613848

It would be nice to update the Signature type to be able to unmarshal from both.