merge: bring phase10-workload-validation forward into sync-diagnostics

Resolutions:
- MetricsRegistry.cpp: keep both <exception> and <limits>; drop
  incrementStateChanges(), which this branch removed on purpose (the
  labelled state_changes_total call site in NetworkOPsImp::setMode
  replaces it, and a compile-time test guards that).
- tests/MetricsRegistry.cpp: constructor-built pipeline wording from
  phase-10, this branch's test list and gauge paragraphs kept; the two
  lifecycle tests now call startAsyncGauges() and pass kTestOptions.
- tests/MetricMacros.cpp: comments name the recording() gate.

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

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

@@ -203,6 +203,7 @@ tests.libxrpl > xrpl.nodestore
 tests.libxrpl > xrpl.peerfinder
 tests.libxrpl > xrpl.protocol
 tests.libxrpl > xrpl.protocol_autogen
+tests.libxrpl > xrpl.rdb
 tests.libxrpl > xrpl.resource
 tests.libxrpl > xrpl.server
 tests.libxrpl > xrpl.shamap