refactor(telemetry): retire the duplicate nodestore_latency gauge

nodestore_latency published six values that nodestore_state already
publishes from the same Database accessors, so the two gauges were
duplicate readings of the same atomics:

  write_count       -> node_writes             getStoreCount()
  read_count        -> node_reads_total        getFetchTotalCount()
  write_duration_us -> node_writes_duration_us getStoreDurationUs()
  read_duration_us  -> node_reads_duration_us  getFetchDurationUs()
  write_mean_us     -> write_mean_us           store duration / count
  read_mean_us      -> read_mean_us            fetch duration / count

nodestore_state is kept because its means go through scaledMean(), which
saturates at INT64_MAX instead of wrapping and omits a mean when the
denominator is zero rather than reporting a misleading 0 us.

Removes registerNodeStoreLatencyGauge, its instrument member, the
metric::nodestoreLatency constant and the lval::nodestore_latency label
namespace. The gauge-over-histogram rationale and the "p99 is not
obtainable" consequence are folded into observeNodeStoreTotals' docs.

Retargets the gauge-contract test onto nodestore_state rather than
deleting it: the scaledMean arithmetic is covered by the static_asserts
in tests/libxrpl/telemetry/MetricsRegistry.cpp, but nothing else asserts
that these named series multiplex onto one instrument keyed by `metric`.
The test now calls the production scaledMean instead of a copy of the
division, and its sub-microsecond case asserts scaledMean's actual
behaviour (a genuine mean of 0 on a zero numerator with a non-zero
count), which differs from the retired gauge's extra numerator guard.

Rewrites both ledger-sync-health copies' panel 38/39 queries and drops
the obsolete claim that the write numerator was never written: all three
concrete store paths call recordStoreDuration, so write_mean_us is live
on an ordinary node. The same stale [import_db] caveat is removed from
the runbook, the 09 reference row and the workload validator's note.

.github/scripts/otel-naming/README.md

@@ -56,7 +56,7 @@ hardcoded allowlist:
 | D    | Every dashboard label resolves to an L1 span attribute, a native-metric label (L6, emitted by MetricsRegistry), or a Prometheus/Grafana builtin. TraceQL scope prefixes (`span.`/`resource.`/…) are stripped before the L1 lookup.                                                                                                                                                                                                                                                                                       |
 | E    | No dotted `xrpl.<domain>.<field>` attribute key in the runbook (only the L1 resource attrs `xrpl.network.*` may be dotted). Span names, filenames, OTel-standard keys, and metric labels are not flagged.                                                                                                                                                                                                                                                                                                                |
 | I    | No string literals as **metric** instrument names or label keys — the mirror of Rule F. Applies to the name passed to an `XRPL_METRIC_*` macro or a `meter->Create*` factory and to the label _keys_ in its label set. Label _values_, descriptions, `*MetricNames.h`, `MetricMacros.h` and test files are exempt. Scoped by metric **family** (first underscore segment): declaring a constant opts that family in, so the metric surface can be converted subsystem by subsystem. Unconverted families warn as Rule L. |
-| J    | Metric instrument names follow the suffix conventions: `lower_snake_case`, no `xrpld_`/`xrpl_` prefix (the exporter adds it), a counter ends `_total`, a histogram ends `_us`/`_ms`/`_seconds`, a gauge does not end `_total`. The instrument **kind** is read from the emit site, never guessed from words in the name — so a multi-series gauge carrying units in its label values (e.g. `nodestore_latency` observing `write_mean_us`) is not a violation.                                                            |
+| J    | Metric instrument names follow the suffix conventions: `lower_snake_case`, no `xrpld_`/`xrpl_` prefix (the exporter adds it), a counter ends `_total`, a histogram ends `_us`/`_ms`/`_seconds`, a gauge does not end `_total`. The instrument **kind** is read from the emit site, never guessed from words in the name — so a multi-series gauge carrying units in its label values (e.g. `nodestore_state` observing `write_mean_us`) is not a violation.                                                              |
 | K    | Every metric named in `docker/telemetry/workload/expected_metrics.json` resolves to a declared constant, so a rename in code cannot leave the workload validator asserting a name nothing emits. PromQL selectors (`m{label="v"}`) and exporter-appended histogram suffixes (`_bucket`/`_count`/`_sum`) are normalized away first; groups fed by another emit path (`statsd_gauges`, `statsd_counters`, `spanmetrics`) are out of scope by design.                                                                       |
 
 Rule F runs **unconditionally** (it is a purely syntactic check on the

.github/scripts/otel-naming/check_otel_naming.py

@@ -1263,9 +1263,9 @@ def instrument_kinds(root: Path, wire_by_symbol: Dict[str, str]) -> Dict[str, st
 
     The kind is what decides which suffix is correct, so it must be read from
     the emit site rather than guessed from the name -- guessing from words like
-    "latency" mislabels a multi-series gauge whose units live in its label
-    VALUES (e.g. `nodestore_latency` observing `write_mean_us`), which is a
-    legitimate shape, not a violation.
+    "latency" or "us" mislabels a multi-series gauge whose units live in its
+    label VALUES (e.g. `nodestore_state` observing `write_mean_us`), which is
+    a legitimate shape, not a violation.
 
     Returns one of `counter`, `histogram`, `gauge`, `updown` per wire name.
     A name whose emit site is not found is absent from the result, so Rule J

.github/scripts/otel-naming/test_check_otel_naming.py

@@ -1184,14 +1184,14 @@ class RuleJMetricSuffixes(unittest.TestCase):
             [],
         )
 
-    def test_gauge_named_latency_is_not_flagged(self):
+    def test_gauge_with_unit_bearing_label_values_is_not_flagged(self):
         # The regression this rule's kind-awareness exists for: a multi-series
-        # GAUGE whose units live in its label VALUES (nodestore_latency
+        # GAUGE whose units live in its label VALUES (nodestore_state
         # observing write_mean_us) must not be read as a mis-suffixed duration.
         self.assertEqual(
             self._run(
-                _mc("nodestoreLatency", "nodestore_latency"),
-                'meter_->CreateInt64ObservableGauge(metric::nodestoreLatency, "d");\n',
+                _mc("nodestoreState", "nodestore_state"),
+                'meter_->CreateInt64ObservableGauge(metric::nodestoreState, "d");\n',
             ),
             [],
         )