Merge branch 'pratik/otel-phase10-workload-validation' into pratik/otel-sync-diagnostics

Brings the MetricsRegistry split onto this branch. The pipeline half is now
xrpl::telemetry::MetricsRegistry in libxrpl; the observable gauges are
xrpl::telemetry::AppMetricGauges in xrpld.

This branch had added its own instrumentation to the pre-split class, so the
merge had to route each addition to the correct half:

- The thirteen gauges added here -- amendment block, cache hit-rate detail,
  clock skew, job-queue saturation, ledger quorum publish, peer ledger supply,
  rotation state, slot census, stall events, sync acquire, sync state, UNL
  quorum, and the cache lock-hold observer -- all land on AppMetricGauges,
  reading the core's meter and validation tracker through it.
- The pipeline additions stay in libxrpl: the consensus round-duration and
  rotation-phase histogram views, the malloc-trim and dns/dial latency bucket
  ladders, the job-stall counter, and the switch from literal metric names to
  the MetricNames.h constants.

Git detected the pre-split MetricsRegistry.cpp and .h as renames of the gauge
files, so both sides' pipeline changes initially landed in the gauge half. They
were moved back, and the result was audited by inventory: every method
definition, instrument creation, view registration, and emitted string from
either side is present, with identical multiplicity.

MetricNames.h moves to include/xrpl/telemetry/ alongside the core. It has no
includes of its own and its two sibling name headers already live there, so
keeping it under src/ would leave an xrpld path in libxrpl's dependency
surface. Nineteen files follow it.

incrementStateChanges() stays removed. The labelled state_changes_total{from,to}
counter this branch introduced replaces it, and the test asserting the method is
absent is kept -- an unlabelled instrument alongside the labelled one would give
Prometheus two conflicting versions of one metric name.

Two tests that drove startAsyncGauges() against a mock ServiceRegistry are
dropped: xrpl_tests links only xrpl.libxrpl and cannot reach the gauge class.

Levelization regenerated. Both xrpld.telemetry loops become bidirectional
rather than one-way; neither is new.

.github/scripts/levelization/results/loops.txt

@@ -8,11 +8,11 @@ Loop: xrpld.app xrpld.shamap
   xrpld.shamap > xrpld.app
 
 Loop: xrpld.app xrpld.telemetry
-  xrpld.app > xrpld.telemetry
+  xrpld.telemetry ~= xrpld.app
 
 Loop: xrpld.overlay xrpld.rpc
   xrpld.rpc ~= xrpld.overlay
 
 Loop: xrpld.overlay xrpld.telemetry
-  xrpld.overlay > xrpld.telemetry
+  xrpld.telemetry ~= xrpld.overlay
 

.github/scripts/levelization/results/ordering.txt

@@ -195,7 +195,6 @@ tests.libxrpl > xrpl.core
 tests.libxrpl > xrpld.app
 tests.libxrpl > xrpld.overlay
 tests.libxrpl > xrpld.rpc
-tests.libxrpl > xrpld.telemetry
 tests.libxrpl > xrpl.json
 tests.libxrpl > xrpl.ledger
 tests.libxrpl > xrpl.net
@@ -254,6 +253,8 @@ xrpl.shamap > xrpl.nodestore
 xrpl.shamap > xrpl.protocol
 xrpl.telemetry > xrpl.basics
 xrpl.telemetry > xrpl.config
+xrpl.telemetry > xrpl.core
+xrpl.telemetry > xrpl.protocol
 xrpl.tx > xrpl.basics
 xrpl.tx > xrpl.core
 xrpl.tx > xrpl.ledger
@@ -308,15 +309,14 @@ xrpld.perflog > xrpl.config
 xrpld.perflog > xrpl.core
 xrpld.perflog > xrpld.app
 xrpld.perflog > xrpld.rpc
-xrpld.perflog > xrpld.telemetry
 xrpld.perflog > xrpl.json
 xrpld.perflog > xrpl.nodestore
 xrpld.perflog > xrpl.protocol
+xrpld.perflog > xrpl.telemetry
 xrpld.rpc > xrpl.basics
 xrpld.rpc > xrpl.config
 xrpld.rpc > xrpl.core
 xrpld.rpc > xrpld.core
-xrpld.rpc > xrpld.telemetry
 xrpld.rpc > xrpl.json
 xrpld.rpc > xrpl.ledger
 xrpld.rpc > xrpl.net