fix(telemetry): make this branch's files compile clean with telemetry off

The metric macros discard their arguments when telemetry is compiled out, so a
file's used-symbol set differs from the one its includes and declarations were
written for. That produced eleven clang-tidy errors here, all from that cause.

- guard <atomic>, <functional> and <memory> in MetricsRegistry.h, and
  <algorithm> and <optional> in DatabaseConfig_test.cpp, to match their uses
- include Journal.h directly in MetricsRegistry.cpp, whose constructor takes a
  beast::Journal by value in both configurations
- compile out recordGetObjectMetrics, its declaration, its call site and the
  two clock reads that feed it, since every statement in it records a metric
- drop two duplicate includes and rename a function-local static constant to
  kEmpty

src/test/nodestore/DatabaseConfig_test.cpp

@@ -33,18 +33,23 @@
 #include <xrpl/nodestore/detail/DatabaseRotatingImp.h>
 #include <xrpl/rdb/DatabaseCon.h>
 
-#include <algorithm>
 #include <atomic>
 #include <chrono>
 #include <cstddef>
 #include <cstdint>
 #include <memory>
-#include <optional>
 #include <string>
 #include <type_traits>
 #include <utility>
 #include <vector>
 
+#ifdef XRPL_ENABLE_TELEMETRY
+// std::ranges::sort / std::ranges::find_if and std::optional / std::nullopt are
+// used only by the gauge-helper suite below, so they are guarded like its uses.
+#include <algorithm>
+#include <optional>
+#endif
+
 namespace xrpl::node_store {
 
 class DatabaseConfig_test : public beast::unit_test::Suite