carrot_impl: add consensus rule for unique output pubkeys in tx

Required by Carrot to mitigate burning bugs, described in section 4.3 of the Carrot spec:
https://github.com/jeffro256/carrot/blob/master/carrot.md#43-transaction-model

Also remove 0-out check in `check_output_types()`, which I added in and technically constitutes a retroactive network split.

Co-authored-by: j-berman <justinberman@protonmail.com>

src/cryptonote_core/blockchain.cpp

@@ -1370,6 +1370,13 @@ bool Blockchain::prevalidate_miner_transaction(const block& b, uint64_t height,
 
   CHECK_AND_ASSERT_MES(check_output_types(b.miner_tx, hf_version), false, "miner transaction has invalid output type(s) in block " << get_block_hash(b));
 
+  // from carrot or v18, require output pubkeys be sorted in strictly increasing lexicographical order
+  const bool tx_is_carrot = !b.miner_tx.vout.empty() && b.miner_tx.vout.at(0).target.type() == typeid(txout_to_carrot_v1);
+  const bool should_enforce_sorted_outputs = hf_version > HF_VERSION_CARROT || tx_is_carrot;
+  if (should_enforce_sorted_outputs) {
+    CHECK_AND_ASSERT_MES(are_transaction_output_pubkeys_sorted(b.miner_tx), false, "miner transaction outputs are not sorted in block " << get_block_hash(b));
+  }
+
   return true;
 }
 //------------------------------------------------------------------
@@ -3691,6 +3698,16 @@ bool Blockchain::check_tx_type_and_version(const transaction& tx, tx_verificatio
     return false;
   }
 
+  // from carrot or v18, require output pubkeys be sorted in strictly increasing lexicographical order
+  const bool tx_is_carrot = !tx.vout.empty() && tx.vout.at(0).target.type() == typeid(txout_to_carrot_v1);
+  const bool should_enforce_sorted_outputs = hf_version > HF_VERSION_CARROT || tx_is_carrot;
+  if (should_enforce_sorted_outputs) {
+    if (!are_transaction_output_pubkeys_sorted(tx)) {
+      tvc.m_invalid_output = true;
+      return false;
+    }
+  }
+
   return true;
 }
 //------------------------------------------------------------------