Fix: Correct ProUpServTx (v2) serialization and parsing (DIP3 / DIP23 compliance)

[LexxXell]

Summary

This PR fixes and modernizes the serialization and deserialization logic for ProUpServTx special transactions according to DIP-3 and DIP-23 specifications (Dash Core ≥ v19).
It also improves backward compatibility with legacy (v1) payloads and adds proper handling of optional Platform fields for mn_type == 1.

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Changes

1. Serialization (serialize)

• ✅ Added structured docstring and explicit field layout (DIP-3/DIP-23 reference).

• ✅ Corrected port endianness → Big-endian (network byte order) for main port.

• ✅ Added optional platformNodeID, platformP2PPort, platformHTTPPort fields for mn_type == 1.

• ✅ Implemented dual-mode signature encoding:

  • v1: CompactSize-prefixed varbytes (legacy BLS).
  • v2: Raw bytes (90–96 B, Basic BLS), no varint prefix.

• ✅ Defensive checks for all field sizes (proTxHash, inputsHash, payloadSig).

• ⚠️ Noted a known discrepancy: platform ports are serialized as LE, although documentation specifies BE — confirmed by actual network payloads.

2. Deserialization (read_vds)

• ✅ Reads mn_type only for version ≥ 2.
• ✅ Reads IP (16 B), port (BE), payout script (varbytes), and 32 B inputsHash.
• ✅ Handles optional platform fields and auto-detects payloadSig length (90 / 96 B).
• ✅ Supports legacy CompactSize signatures (v1).
• ✅ Converts IPv6-mapped IPv4 addresses to readable strings.

3. __str__ improvements

• ✅ Extended string representation with:

  • mn_type
  • optional platformNodeID and platform ports

• ✅ Improved readability and conditional formatting for optional fields.

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Compatibility

• Backward-compatible with all previously serialized v1 ProUpServTx payloads.
• Forward-compatible with current Dash Core v20+ ProUpServTx payloads (Basic BLS).
• No impact on other special transaction types (ProRegTx, ProUpRegTx, ProUpRevTx).

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Testing

• Added and verified round-trip tests using real raw transactions:

  • ✅ ProUpServTx (v2, mn_type = 1)
  • ✅ ProRegTx (v2)

• Verified correct txid() against known hashes.

• Confirmed serialized payload matches expected field layout and byte order.

• Checked fallback handling for legacy payloads (CompactSize + varbytes signature).

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Notes

• The platform port endianness inconsistency remains intentionally preserved to match real on-chain payloads.
• Further unit tests for ProUpRegTx and ProUpRevTx are planned for a future PR.

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References

• [DIP-0003: Deterministic Masternode Lists](https://github.com/dashpay/dips/blob/master/dip-0003.md)
• [DIP-0023: Dash Platform & BLS Basic Scheme](https://github.com/dashpay/dips/blob/master/dip-0023.md)
• Dash Core v19+ source (src/evo/specialtxes.cpp, bls_basic_scheme.cpp)

[pshenmic]

Should not be here I believe

[LexxXell]

yep
fixed