fix(telemetry): use underscore attr names and SpanNames constants in Phase 4

- tempo.yaml: align consensus filter tags with emitted keys
  (consensus_mode, consensus_round, ledger_seq) instead of dotted form
- haveConsensus(): set span attributes before early-return paths so the
  consensus.check span carries diagnostics even when consensus is not reached
- replace hardcoded consensus phase/result/vote literals with
  ConsensusSpanNames.h val constants; add val::phaseOpen/Establish/Accepted
- ConsensusReceiveTracing.h: use canonical consensus::span constants instead
  of duplicate inline detail:: names
- SpanGuardFactory test: use rpc_span / consensus::span constants now that
  levelization permits the dependency

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker/telemetry/grafana/provisioning/datasources/tempo.yaml

@@ -126,17 +126,17 @@ datasources:
             type: dynamic
           # Phase 4: Consensus tracing filters
           - id: consensus-mode
-            tag: xrpl.consensus.mode
+            tag: consensus_mode
             operator: "="
             scope: span
             type: static
           - id: consensus-round
-            tag: xrpl.consensus.round
+            tag: consensus_round
             operator: "="
             scope: span
             type: dynamic
           - id: consensus-ledger-seq
-            tag: xrpl.ledger.seq
+            tag: ledger_seq
             operator: "="
             scope: span
             type: static