Prettify uptime duration in log lines

Produces strings such as:

    [+1h09m12.475s]

instead of:

    [+4152475 ms]

llarp/util/logging/logger_internal.cpp

@@ -7,9 +7,33 @@ namespace llarp
   std::ostream&
   operator<<(std::ostream& out, const log_timestamp& ts)
   {
+    std::chrono::milliseconds delta{ts.delta};
+    auto h = std::chrono::duration_cast< std::chrono::hours >(delta);
+    delta -= h;
+    auto m = std::chrono::duration_cast< std::chrono::minutes >(delta);
+    delta -= m;
+    auto s = std::chrono::duration_cast< std::chrono::seconds >(delta);
+    delta -= s;
+    auto ms = delta;
     std::chrono::time_point< std::chrono::system_clock,
                              std::chrono::milliseconds >
         now{std::chrono::milliseconds{ts.now}};
-    return date::operator<<(out, now) << " UTC [+" << ts.delta << " ms]";
+    date::operator<<(out, now) << " UTC [+";
+    auto old_fill = out.fill('0');
+    if(h > 0h)
+    {
+      out << h.count() << 'h';
+      out.width(2);  // 0-fill minutes if we have hours
+    }
+    if(h > 0h || m > 0min)
+    {
+      out << m.count() << 'm';
+      out.width(2);  // 0-fill seconds if we have minutes
+    }
+    out << s.count() << '.';
+    out.width(3);
+    out << ms.count();
+    out.fill(old_fill);
+    return out << "s]";
   }
 }  // namespace llarp