Fix base58 functions and protobuf build - #19

Wires the ZIP-32 §6.1 seed fingerprint binding into the python-keepkey
client to mirror the firmware-side validation.

  device-protocol submodule
    - URL: keepkey/device-protocol -> BitHighlander/device-protocol
      (zcash work pins to fork master while seed_fingerprint sits in
      long-term review for upstream; revert when upstream merges.)
    - pin: d0b8d80 -> 4337c452 (BitHighlander/master with PR #27 merged).
    - messages_zcash_pb2.py regenerated via docker_build_pb.sh
      (kktech/firmware:v8 → libprotoc 3.5.1, the canonical toolchain).
      Selective regen — other pb2 files are intentionally NOT
      regenerated because they currently include content from
      BitHighlander/device-protocol open PRs (#18 SolanaTokenInfo,
      #19 TRON clear-signing, #20 TON clear-signing, #21
      EthereumTxMetadata). Until those merge, regenerating them
      against current master would back out work that the existing
      python-keepkey client relies on.

  keepkeylib/zcash.py (new)
    calculate_seed_fingerprint(seed) -> 32 bytes
      Pure-Python helper. BLAKE2b-256("Zcash_HD_Seed_FP",
      I2LEBSP_8(len) || seed). Matches the firmware C
      implementation byte-for-byte and the keystone3-firmware
      reference vector
        seed = 000102...1f
        fp   = deff604c246710f7176dead02aa746f2fd8d5389f7072556dcb555fdbe5e3ae3

  keepkeylib/client.py
    zcash_display_address  — add expected_seed_fingerprint kwarg
    zcash_sign_pczt         — add expected_seed_fingerprint kwarg
    Both pass through unchanged when the kwarg is None
    (backward compatible).

  tests/test_msg_zcash_seed_fingerprint.py (new)
    Pure-Python helper:
      - reference vector (Keystone3 cross-check)
      - rejects all-zero, all-0xFF, short, long
    Device-backed:
      - GetOrchardFVK returns non-empty seed_fingerprint
      - fingerprint stable across accounts (bound to seed, not account)
      - DisplayAddress: matching expected_seed_fingerprint succeeds,
        response carries seed_fingerprint
      - DisplayAddress: wrong expected_seed_fingerprint rejected
      - DisplayAddress: omitting expected_seed_fingerprint still works
      - SignPCZT: wrong expected_seed_fingerprint rejected before
        any signing crypto runs