Merge bitcoin#29647: Avoid divide-by-zero in header sync logs when NodeClock is behind

fa4d98b Avoid divide-by-zero in header sync logs when NodeClock is behind (MarcoFalke)
fa58550 refactor: Modernize header sync logs (MarcoFalke)

Pull request description:

  The log may be confusing, when the NodeClock is behind the current header tip.

  Fix it, by assuming the NodeClock is never behind the current header tip.

ACKs for top commit:
  sipa:
    utACK fa4d98b
  sr-gi:
    tACK [fa4d98b](bitcoin@fa4d98b)
  achow101:
    ACK fa4d98b
  tdb3:
    ACK fa4d98b

Tree-SHA512: 3c5aee4030af387695918c5238012c972ebf850b52e956b5f74590cd7fd4eff0b3e593d411e3eb2a0bb12294af8dc6fbe320f90e4c261399b65a404ff3c3cbd9

Author: achow101

src/validation.cpp

@@ -4234,9 +4234,10 @@ bool ChainstateManager::ProcessNewBlockHeaders(const std::vector<CBlockHeader>&
     if (NotifyHeaderTip(*this)) {
         if (IsInitialBlockDownload() && ppindex && *ppindex) {
             const CBlockIndex& last_accepted{**ppindex};
-            const int64_t blocks_left{(GetTime() - last_accepted.GetBlockTime()) / GetConsensus().nPowTargetSpacing};
+            int64_t blocks_left{(NodeClock::now() - last_accepted.Time()) / GetConsensus().PowTargetSpacing()};
+            blocks_left = std::max<int64_t>(0, blocks_left);
             const double progress{100.0 * last_accepted.nHeight / (last_accepted.nHeight + blocks_left)};
-            LogPrintf("Synchronizing blockheaders, height: %d (~%.2f%%)\n", last_accepted.nHeight, progress);
+            LogInfo("Synchronizing blockheaders, height: %d (~%.2f%%)\n", last_accepted.nHeight, progress);
         }
     }
     return true;
@@ -4260,9 +4261,10 @@ void ChainstateManager::ReportHeadersPresync(const arith_uint256& work, int64_t
     bool initial_download = IsInitialBlockDownload();
     GetNotifications().headerTip(GetSynchronizationState(initial_download), height, timestamp, /*presync=*/true);
     if (initial_download) {
-        const int64_t blocks_left{(GetTime() - timestamp) / GetConsensus().nPowTargetSpacing};
+        int64_t blocks_left{(NodeClock::now() - NodeSeconds{std::chrono::seconds{timestamp}}) / GetConsensus().PowTargetSpacing()};
+        blocks_left = std::max<int64_t>(0, blocks_left);
         const double progress{100.0 * height / (height + blocks_left)};
-        LogPrintf("Pre-synchronizing blockheaders, height: %d (~%.2f%%)\n", height, progress);
+        LogInfo("Pre-synchronizing blockheaders, height: %d (~%.2f%%)\n", height, progress);
     }
 }