Merge branch 'pratik/otel-phase2-rpc-tracing' into pratik/otel-phase3-tx-tracing

Bring phase-2 forward into phase 3 (transaction tracing). Phase 3 introduces
TxSpanNames.h, TxQSpanNames.h, and TxApplySpanNames.h.

Conflict resolution:
- TxQ.cpp: kept phase-3's txq_span-based instrumentation (phase-2 had none).
  Dropped the orphaned `NumberSO{... fixUniversalNumber}` line — develop's
  #5962 (Retire fixUniversalNumber) removed that symbol repo-wide; the
  conflict block had carried one stale copy that would not compile.
- 05/08/OpenTelemetryPlan.md: dropped the deleted 04-code-samples / POC_taskList
  references (carried from phase-2), kept phase-3's new secure-OTel.md doc rows,
  section, and Mermaid node/edge/style. Config code block -> prose; merged the
  secure-OTel hardening pointer with the authoritative-config prose.
- Phase3_taskList.md: removed the "dotted keys for readability" note that came
  from phase-2 — phase 3 already uses the underscore keys.

Reviewed by code-review agents: telemetry instrumentation intact, naming check
green (47 keys across 7 *SpanNames.h headers), no conflict markers.

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

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

@@ -253,7 +253,6 @@ xrpl.shamap > xrpl.basics
 xrpl.shamap > xrpl.nodestore
 xrpl.shamap > xrpl.protocol
 xrpl.telemetry > xrpl.config
-xrpl.telemetry > xrpld.consensus
 xrpl.tx > xrpl.basics
 xrpl.tx > xrpl.core
 xrpl.tx > xrpl.ledger