bench: basic block filter index initial sync

Introduce benchmark for the block filter index sync.
And makes synchronous 'Sync()' mechanism accessible.

src/index/base.cpp

@@ -141,7 +141,7 @@ static const CBlockIndex* NextSyncBlock(const CBlockIndex* pindex_prev, CChain&
     return chain.Next(chain.FindFork(pindex_prev));
 }
 
-void BaseIndex::ThreadSync()
+void BaseIndex::Sync()
 {
     const CBlockIndex* pindex = m_best_block_index.load();
     if (!m_synced) {
@@ -394,7 +394,7 @@ bool BaseIndex::StartBackgroundSync()
 {
     if (!m_init) throw std::logic_error("Error: Cannot start a non-initialized index");
 
-    m_thread_sync = std::thread(&util::TraceThread, GetName(), [this] { ThreadSync(); });
+    m_thread_sync = std::thread(&util::TraceThread, GetName(), [this] { Sync(); });
     return true;
 }
 

src/index/base.h

@@ -78,13 +78,6 @@ private:
     std::thread m_thread_sync;
     CThreadInterrupt m_interrupt;
 
-    /// Sync the index with the block index starting from the current best block.
-    /// Intended to be run in its own thread, m_thread_sync, and can be
-    /// interrupted with m_interrupt. Once the index gets in sync, the m_synced
-    /// flag is set and the BlockConnected ValidationInterface callback takes
-    /// over and the sync thread exits.
-    void ThreadSync();
-
     /// Write the current index state (eg. chain block locator and subclass-specific items) to disk.
     ///
     /// Recommendations for error handling:
@@ -152,9 +145,16 @@ public:
     /// validation interface so that it stays in sync with blockchain updates.
     [[nodiscard]] bool Init();
 
-    /// Starts the initial sync process.
+    /// Starts the initial sync process on a background thread.
     [[nodiscard]] bool StartBackgroundSync();
 
+    /// Sync the index with the block index starting from the current best block.
+    /// Intended to be run in its own thread, m_thread_sync, and can be
+    /// interrupted with m_interrupt. Once the index gets in sync, the m_synced
+    /// flag is set and the BlockConnected ValidationInterface callback takes
+    /// over and the sync thread exits.
+    void Sync();
+
     /// Stops the instance from staying in sync with blockchain updates.
     void Stop();