Phase 4a: Establish-phase gap fill & cross-node correlation

Add full consensus tracing with deterministic trace ID correlation
and establish-phase instrumentation:

- Deterministic trace_id from previousLedger.id() for cross-node
  correlation (switchable via consensus_trace_strategy config)
- Round-to-round span links (follows-from) for causal chaining
- Establish phase spans with convergence tracking, dispute resolution
  events, and threshold escalation attributes
- Validation spans with links to round spans (thread-safe via
  roundSpanContext_ snapshot for jtACCEPT cross-thread access)
- Mode change spans for proposing/observing transitions
- New startSpan overload with span links in Telemetry interface
- XRPL_TRACE_ADD_EVENT macro with do-while(0) safety wrapper
- Config validation for consensus_trace_strategy
- Test adaptor (csf::Peer) updated with getTelemetry() stub

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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

@@ -92,6 +92,7 @@ test.csf > xrpl.basics
 test.csf > xrpld.consensus
 test.csf > xrpl.json
 test.csf > xrpl.protocol
+test.csf > xrpl.telemetry
 test.json > test.jtx
 test.json > xrpl.json
 test.jtx > xrpl.basics
@@ -233,8 +234,10 @@ xrpld.app > xrpl.shamap
 xrpld.app > xrpl.telemetry
 xrpld.app > xrpl.tx
 xrpld.consensus > xrpl.basics
+xrpld.consensus > xrpld.telemetry
 xrpld.consensus > xrpl.json
 xrpld.consensus > xrpl.protocol
+xrpld.consensus > xrpl.telemetry
 xrpld.core > xrpl.basics
 xrpld.core > xrpl.core
 xrpld.core > xrpl.json