feat(telemetry): add Phase 4 consensus tracing with SpanGuard API

Instrument the consensus subsystem with OpenTelemetry spans covering
the full round lifecycle: round start, establish phase, proposal send,
ledger close, position updates, consensus check, accept, validation
send, and mode changes.

Key design choices adapted from the original Phase 4 implementation
to the new SpanGuard factory pattern introduced in Phase 3:

- Add SpanGuard::hashSpan() for category-gated hash-derived trace IDs
  (consensus round spans share trace_id across validators via ledger hash)
- Add SpanGuard::addEvent() overload with key-value attribute pairs
  (used for dispute.resolve events during position updates)
- Add ConsensusSpanNames.h with compile-time span name constants
  following the colocated *SpanNames.h pattern from Phase 3
- Add consensusTraceStrategy config option ("deterministic"/"attribute")
  for cross-node trace correlation strategy selection
- Use SpanGuard::linkedSpan() for follows-from relationships between
  consecutive rounds and cross-thread validation spans
- Use SpanGuard::captureContext() for thread-safe context propagation
  from consensus thread to jtACCEPT worker thread

Spans produced: consensus.round, consensus.proposal.send,
consensus.ledger_close, consensus.establish, consensus.update_positions,
consensus.check, consensus.accept, consensus.accept.apply,
consensus.validation.send, consensus.mode_change

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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

@@ -101,6 +101,7 @@ test.core > xrpl.server
 test.csf > xrpl.basics
 test.csf > xrpld.consensus
 test.csf > xrpl.json
+test.csf > xrpl.telemetry
 test.csf > xrpl.ledger
 test.csf > xrpl.protocol
 test.json > test.jtx
@@ -194,6 +195,8 @@ tests.libxrpl > xrpl.json
 tests.libxrpl > xrpl.net
 tests.libxrpl > xrpl.protocol
 tests.libxrpl > xrpl.protocol_autogen
+tests.libxrpl > xrpl.telemetry
+tests.libxrpl > xrpld.telemetry
 xrpl.conditions > xrpl.basics
 xrpl.conditions > xrpl.protocol
 xrpl.core > xrpl.basics
@@ -253,6 +256,8 @@ xrpld.consensus > xrpl.basics
 xrpld.consensus > xrpl.json
 xrpld.consensus > xrpl.ledger
 xrpld.consensus > xrpl.protocol
+xrpld.consensus > xrpl.telemetry
+xrpld.consensus > xrpld.telemetry
 xrpld.core > xrpl.basics
 xrpld.core > xrpl.core
 xrpld.core > xrpl.net