Merge bitcoin/bitcoin#34615: mempool: expose optimality of mempool to log / rpc

a9e59f7d95 rpc: add optimal result to getmempoolinfo (Greg Sanders)
a3fb3dd55c mempool: log if we detect a non-optimal mempool (Greg Sanders)

Pull request description:

  Post-SFL #34023 I don't think we expect the mempool to be unordered for long periods of time. If we consider it likely to be a serious regression in production, it would be useful to expose the fact  that the mempool is not known to be optimal.

  1. do a MEMPOOL log after any `DoWork()` returns false, meaning non-optimal
  2. expose it via getmempoolinfo, by calling `DoWork(0)`, which does nothing but return known-optimality

  I'm not wedded to either approach, I just think something is better than nothing for the next release.

ACKs for top commit:
  ajtowns:
    ACK a9e59f7d95
  ismaelsadeeq:
    reACK a9e59f7d95 [c89b93b95..a9e59f7d95](c89b93b958..a9e59f7d95) fixed typo, added more logging for block/reorg additions to mempool, and fixed brittle test case.
  sedited:
    ACK a9e59f7d95
  sipa:
    ACK a9e59f7d95

Tree-SHA512: 1560ad21cc1606df7279c102f35f61d4555c0ac920f02208b2a6eb89b14d7e22befb6d7f510a00a9074c2f9931f32e9af86bcea3a8dd9a1d947b0398c84666dd

src/rpc/mempool.cpp

@@ -1050,6 +1050,7 @@ UniValue MempoolInfoToJSON(const CTxMemPool& pool)
     ret.pushKV("maxdatacarriersize", pool.m_opts.max_datacarrier_bytes.value_or(0));
     ret.pushKV("limitclustercount", pool.m_opts.limits.cluster_count);
     ret.pushKV("limitclustersize", pool.m_opts.limits.cluster_size_vbytes);
+    ret.pushKV("optimal", pool.m_txgraph->DoWork(0)); // 0 work is a quick check for known optimality
     return ret;
 }
 
@@ -1076,6 +1077,7 @@ static RPCHelpMan getmempoolinfo()
                 {RPCResult::Type::NUM, "maxdatacarriersize", "Maximum number of bytes that can be used by OP_RETURN outputs in the mempool"},
                 {RPCResult::Type::NUM, "limitclustercount", "Maximum number of transactions that can be in a cluster (configured by -limitclustercount)"},
                 {RPCResult::Type::NUM, "limitclustersize", "Maximum size of a cluster in virtual bytes (configured by -limitclustersize)"},
+                {RPCResult::Type::BOOL, "optimal", "If the mempool is in a known-optimal transaction ordering"},
             }},
         RPCExamples{
             HelpExampleCli("getmempoolinfo", "")