wallet/rpc: monotonic timers and a quieter default slow-walk line

Review follow-ups to the GetFilteredNotes / RPC timing logs:

- Time with std::chrono::steady_clock instead of GetTimeMicros(), which
  is the system clock. A wall-clock step otherwise writes false
  ">= 500ms" lines unconditionally; on a WSL2 host the clock was seen
  stepping +3.6s every ~32s.
- A long-poll getblocktemplate deliberately blocks (with cs_main
  released) until a new block arrives, so it is logged only under
  -debug=bench.
- Log the method as "RPC method=<name> took <n>ms". A bare " rescan "
  token followed by "<n>ms" matches ObsidianDragon's rescan-finished
  log heuristic.
- The always-on slow-walk line keeps just the filters and the walk
  time; the wallet-size counts (txs, notes, spent, entries) are logged
  only with -debug=bench, so a shared debug.log doesn't carry them.
- The -txindex=0 startup line names the version.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/wallet/wallet.cpp

@@ -45,6 +45,7 @@
 #include <limits>
 #include <system_error>
 #include <thread>
+#include <chrono>
 #include <atomic>
 #include <mutex>
 #include "zcash/zip32.h"
@@ -5762,7 +5763,7 @@ void CWallet::GetFilteredNotes(
 
     // Every caller already holds LOCK2, so the lock above never waits and this times the walk alone.
     // Time spent waiting for the locks shows up in the RPC's own "took" line (rpc/server.cpp).
-    const int64_t nTimeStart = GetTimeMicros();
+    const std::chrono::steady_clock::time_point walkStart = std::chrono::steady_clock::now();
     const size_t nEntriesBefore = saplingEntries.size();
     unsigned int nTxs = 0, nNotes = 0, nSpent = 0;
 
@@ -5850,12 +5851,16 @@ void CWallet::GetFilteredNotes(
     }
 
     // A slow walk holds cs_main long enough to stall block connection, so it is always logged; a
-    // fast one only with -debug=bench (the balance RPCs run it on every GUI poll).
-    const int64_t nWalkMs = (GetTimeMicros() - nTimeStart) / 1000;
-    if (nWalkMs >= 500 || LogAcceptCategory("bench")) {
+    // fast one only with -debug=bench (the balance RPCs run it on every GUI poll). The wallet-size
+    // counts go to the default log only with -debug=bench too.
+    const int64_t nWalkMs = std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::steady_clock::now() - walkStart).count();
+    if (LogAcceptCategory("bench")) {
         LogPrintf("%s: minDepth=%d ignoreSpent=%d requireSpendingKey=%d ignoreLocked=%d txs=%u/%u notes=%u spent=%u entries=%u walk=%dms\n",
                   __func__, minDepth, ignoreSpent, requireSpendingKey, ignoreLocked, nTxs, (unsigned int)mapWallet.size(),
                   nNotes, nSpent, (unsigned int)(saplingEntries.size() - nEntriesBefore), nWalkMs);
+    } else if (nWalkMs >= 500) {
+        LogPrintf("%s: minDepth=%d ignoreSpent=%d requireSpendingKey=%d ignoreLocked=%d walk=%dms\n",
+                  __func__, minDepth, ignoreSpent, requireSpendingKey, ignoreLocked, nWalkMs);
     }
 }