Draft: Add `signstar-request-signature` and signing hash states

Adds signstar-request-signature binary which produces signing requests files:

{
    "required": {
        "input": {
            "type": "sha2-0.11-SHA512-state",
            "content": [8,201,188,243,103,230,9,106,59,167,202,132,133,174,103,187,43,248,148,254,114,243,110,60,241,54,29,95,58,245,79,165,209,130,230,173,127,82,14,81,31,108,62,43,140,104,5,155,107,189,65,251,171,217,131,31,121,33,126,19,25,205,224,91,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,64,20,73,32,108,105,107,101,32,115,116,114,97,119,98,101,114,114,105,101,115,10,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
        },
        "output": {
            "type": "OpenPGPv4"
        }
    },
    "optional": {
        "request-time": 1728913277,
        "XHy1dHj": "https://gitlab.archlinux.org/archlinux/signstar/-/merge_requests/43"
    }
}

And then adds nethsm openpgp sign-state command which ingests the signing request JSON file and produces OpenPGP signature.

The entire flow looks like this:

signstar-request-signature < file.txt | nethsm openpgp sign-state signing1 > file.txt.pgp

The resulting signature has file.txt digest embedded inside.

Signature Packet, new CTB, 216 bytes
    Version: 4
    Type: Binary
    Pk algo: EdDSA
    Hash algo: SHA512
    Hashed area:
      Signature creation time: 2024-09-12 13:37:57 UTC
      Issuer: 75053BB045A49049
      Issuer Fingerprint: 81057E2707FB660398FEA88275053BB045A49049
      Notation: data-digest@archlinux.org
        00000000  55 b9 56 f9 bb 40 75 2f  a3 28 c9 35 23 a9 77 5a
        00000010  a8 4e 1d 20 14 37 27 79  fd cb 9f 52 55 28 e9 1a
        00000020  d0 0d 6f 3d 5d 64 c7 1f  b9 8c c3 72 5c 76 6c ed
        00000030  64 98 d4 b1 bd 38 92 cc  89 4c eb 1f 65 01 13 37
    Digest prefix: DE0C
    Level: 0 (signature over data)