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>

src/test/csf/Peer.h

@@ -24,6 +24,7 @@
 #include <xrpl/beast/utility/WrappedSink.h>
 #include <xrpl/json/json_value.h>
 #include <xrpl/json/json_writer.h>
+#include <xrpl/telemetry/SpanGuard.h>
 
 #include <boost/container/flat_map.hpp>
 #include <boost/container/flat_set.hpp>
@@ -700,6 +701,15 @@ struct Peer
     {
     }
 
+    // The generic engine parents its phase spans under the round span via
+    // this context; the simulator runs without telemetry, so return an
+    // invalid context and no phase span is created.
+    static telemetry::SpanContext
+    roundSpanContext()
+    {
+        return {};
+    }
+
     // Share a message by broadcasting to all connected peers
     template <class M>
     void