wallet: Track scanning duration

src/wallet/wallet.h

@@ -596,6 +596,7 @@ class CWallet final : public CCryptoKeyStore, private interfaces::Chain::Notific
 private:
     std::atomic<bool> fAbortRescan{false};
     std::atomic<bool> fScanningWallet{false}; // controlled by WalletRescanReserver
+    std::atomic<int64_t> m_scanning_start{0};
     std::mutex mutexScanning;
     friend class WalletRescanReserver;
 
@@ -820,6 +821,7 @@ public:
     void AbortRescan() { fAbortRescan = true; }
     bool IsAbortingRescan() { return fAbortRescan; }
     bool IsScanning() { return fScanningWallet; }
+    int64_t ScanningDuration() const { return fScanningWallet ? GetTimeMillis() - m_scanning_start : 0; }
 
     /**
      * keystore implementation
@@ -1241,6 +1243,7 @@ public:
         if (m_wallet->fScanningWallet) {
             return false;
         }
+        m_wallet->m_scanning_start = GetTimeMillis();
         m_wallet->fScanningWallet = true;
         m_could_reserve = true;
         return true;