fix(telemetry): satisfy clang-tidy on the noopMeter() helper

Static constants take the k prefix (readability-identifier-naming), and
SpanGuardScope.cpp no longer names anything from <opentelemetry/metrics/noop.h>
since it calls noopMeter(). Both fail CI under warnings-as-errors.

The helper's docstring also claimed NoopMeterProvider hides the base
two-argument GetMeter; it declares that overload itself, so the only
detail worth sharing is the version.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

include/xrpl/telemetry/Telemetry.h

@@ -141,11 +141,9 @@ inline constexpr std::string_view kMeterVersion{"1.0.0"};
  * it: telemetry disabled, or an exporter that failed to build. Callers then
  * need no null check, because an instrument always comes back.
  *
- * Two details are easy to get wrong alone, which is why this is shared: the
- * provider must be reached through a base `MeterProvider` pointer, because
- * `NoopMeterProvider`'s override hides the base class's defaulted overload;
- * and the version must be @ref kMeterVersion, or the meter identity differs
- * from the one the histogram views select on.
+ * Shared so every caller passes the same version, @ref kMeterVersion. A
+ * different version gives a different meter identity from the one the
+ * histogram views select on.
  *
  * @param name Instrumentation scope name to report.
  * @return An inert meter. Never empty.