fix(telemetry): restore injectCurrentContextToProtobuf decl; re-parent open/establish spans under round; correct childSpan names

Post-review fixes for the SpanGuard scope-leak change:
- SpanGuard.h: restore the injectCurrentContextToProtobuf real-class
  declaration, its #else no-op stub, and the protocol::TraceContext
  forward-declaration dropped during the 3->4 union merge (compile break).
- Re-parent consensus.phase.open and consensus.establish under the round
  span via a new RCLConsensus::Adaptor::roundSpanContext() accessor: the
  round span is now detached, so ambient parenting no longer works; the
  phase spans link explicitly to the captured round context. csf::Peer
  gains a matching no-op accessor so the generic engine still compiles.
- Switch five childSpan(op::X, ctx) sites to the full consensus::span::X
  constants: childSpan(name, ctx) takes the name verbatim, so the suffix-
  only op:: constants emitted short, non-dotted span names.
- TestTelemetry mock: add getConsensusTraceStrategy() override (base pure
  virtual introduced on this branch) so the mock is not abstract.
- validate(): rewrite the trace_context comment to drop attack-surface
  framing and the PR-discussion reference.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

include/xrpl/telemetry/SpanGuard.h

@@ -170,6 +170,10 @@
 #include <string_view>
 #include <utility>
 
+namespace protocol {
+class TraceContext;
+}  // namespace protocol
+
 namespace xrpl::telemetry {
 
 /**
@@ -436,6 +440,20 @@ public:
     [[nodiscard]] TraceBytes
     getTraceBytes() const;
 
+    /**
+     * Inject the calling thread's currently-active OTel context into a
+     * protobuf TraceContext message for cross-node propagation.
+     *
+     * Encapsulates `RuntimeContext::GetCurrent()` + `injectToProtobuf`
+     * so callers in app-layer code (e.g. RCLConsensus broadcasting
+     * TMProposeSet / TMValidation) don't depend on any OTel headers.
+     * No-op if telemetry is disabled or no span is active.
+     *
+     * @param proto The protobuf TraceContext to populate.
+     */
+    static void
+    injectCurrentContextToProtobuf(protocol::TraceContext& proto);
+
     // --- Attribute setters (explicit overloads, no OTel types) ---------
 
     /**
@@ -613,6 +631,11 @@ public:
     {
         return {};
     }
+
+    static void
+    injectCurrentContextToProtobuf(protocol::TraceContext&)
+    {
+    }
     // NOLINTEND(readability-convert-member-functions-to-static)
 
     void