feat(llmq): llmq_25_67 for Platform (Testnet only) (#5225)

- Added new LLMQ type `llmq_25_67`
- The above LLMQ is added only for Testnet and it is activated with v19
fork.

- [x] I have performed a self-review of my own code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have added or updated relevant unit/integration/functional/e2e
tests
- [ ] I have made corresponding changes to the documentation

**For repository code-owners and collaborators only**
- [x] I have assigned this pull request to a milestone

---------

Co-authored-by: pasta <pasta@dashboost.org>

doc/release-notes-5225.md

@@ -0,0 +1,10 @@
+Testnet Breaking Changes
+------------------------
+
+A new testnet only LLMQ has been added. This LLMQ is of the type LLMQ_25_67; this LLMQ is only active on testnet. 
+This LLMQ will not remove the LLMQ_100_67 from testnet; however that quorum (likely) will not form and will perform no role.
+See the [diff](https://github.com/dashpay/dash/pull/5225/files#diff-e70a38a3e8c2a63ca0494627301a5c7042141ad301193f78338d97cb1b300ff9R451-R469) for specific parameters of the LLMQ.
+
+This LLMQ will become active at the height of 847000. **This will be a breaking change and a hard fork for testnet**
+This LLMQ is not activated with the v19 hardfork; as such testnet will experience two hardforks. One at height 847000,
+and the other to be determined by the BIP9 hard fork process.

src/chainparams.cpp

@@ -523,10 +523,11 @@ public:
         AddLLMQ(Consensus::LLMQType::LLMQ_400_60);
         AddLLMQ(Consensus::LLMQType::LLMQ_400_85);
         AddLLMQ(Consensus::LLMQType::LLMQ_100_67);
+        AddLLMQ(Consensus::LLMQType::LLMQ_25_67);
         consensus.llmqTypeChainLocks = Consensus::LLMQType::LLMQ_50_60;
         consensus.llmqTypeInstantSend = Consensus::LLMQType::LLMQ_50_60;
         consensus.llmqTypeDIP0024InstantSend = Consensus::LLMQType::LLMQ_60_75;
-        consensus.llmqTypePlatform = Consensus::LLMQType::LLMQ_100_67;
+        consensus.llmqTypePlatform = Consensus::LLMQType::LLMQ_25_67;
         consensus.llmqTypeMnhf = Consensus::LLMQType::LLMQ_50_60;
 
         fDefaultConsistencyChecks = false;

src/llmq/params.h

@@ -19,6 +19,7 @@ enum class LLMQType : uint8_t {
     LLMQ_400_85 = 3, // 400 members, 340 (85%) threshold, one every 24 hours
     LLMQ_100_67 = 4, // 100 members, 67 (67%) threshold, one per hour
     LLMQ_60_75 = 5,  // 60 members, 45 (75%) threshold, one every 12 hours
+    LLMQ_25_67 = 6, // 25 members, 67 (67%) threshold, one per hour
 
     // for testing only
     LLMQ_TEST = 100, // 3 members, 2 (66%) threshold, one per hour. Params might differ when -llmqtestparams is used
@@ -106,7 +107,7 @@ struct LLMQParams {
 };
 
 
-static constexpr std::array<LLMQParams, 11> available_llmqs = {
+static constexpr std::array<LLMQParams, 12> available_llmqs = {
 
     /**
      * llmq_test
@@ -388,6 +389,33 @@ static constexpr std::array<LLMQParams, 11> available_llmqs = {
         .recoveryMembers = 50,
     },
 
+    /**
+     * llmq_25_67
+     * This quorum is deployed on Testnet and requires
+     * 25 participants
+     *
+     * Used by Dash Platform
+     */
+    LLMQParams{
+        .type = LLMQType::LLMQ_25_67,
+        .name = "llmq_25_67",
+        .useRotation = false,
+        .size = 25,
+        .minSize = 22,
+        .threshold = 17,
+
+        .dkgInterval = 24, // one DKG per hour
+        .dkgPhaseBlocks = 2,
+        .dkgMiningWindowStart = 10, // dkgPhaseBlocks * 5 = after finalization
+        .dkgMiningWindowEnd = 18,
+        .dkgBadVotesThreshold = 22,
+
+        .signingActiveQuorumCount = 24, // a full day worth of LLMQs
+
+        .keepOldConnections = 25,
+        .recoveryMembers = 12,
+    },
+
 }; // available_llmqs
 
 } // namespace Consensus

src/llmq/utils.cpp

@@ -23,6 +23,8 @@
 
 #include <optional>
 
+static constexpr int TESTNET_LLMQ_25_67_ACTIVATION_HEIGHT = 847000;
+
 namespace llmq
 {
 
@@ -915,6 +917,11 @@ bool IsQuorumTypeEnabledInternal(Consensus::LLMQType llmqType, const CQuorumMana
             }
             break;
         }
+        case Consensus::LLMQType::LLMQ_25_67:
+            if (pindex->nHeight < TESTNET_LLMQ_25_67_ACTIVATION_HEIGHT) {
+                return false;
+            }
+            break;
         default:
             throw std::runtime_error(strprintf("%s: Unknown LLMQ type %d", __func__, static_cast<uint8_t>(llmqType)));
     }