docs(consensus): drop pre-squash comparisons from the tracing comments

Both comments pointed at a state the squash merge does not publish.

- Consensus.h: 'yields a null guard, same as before' had no antecedent in the
  round or the function. Say instead that a null guard makes the setAttribute
  calls below no-ops, which is what SpanGuard's impl_ guard does.
- ConsensusSpanLabels.h: 'Split from ConsensusSpanNames.h' describes a split
  performed entirely within this change; both headers first appear here. The
  dependency rationale and the diagram are unchanged.

Comments only, no behaviour change.

include/xrpl/consensus/Consensus.h

@@ -1689,8 +1689,9 @@ Consensus<Adaptor>::updateOurPositions(std::unique_ptr<std::stringstream> const&
     // NOLINTBEGIN(bugprone-unchecked-optional-access) assert above
     using namespace telemetry;
     // Child of the establish span via its captured context (establishSpan_ is
-    // a thread-free SpanGuard, so parent explicitly via its context). Null
-    // context (establish not started) yields a null guard, same as before.
+    // a thread-free SpanGuard, so parent explicitly via its context). A null
+    // context — the establish phase has not started — yields a null guard, so
+    // the setAttribute calls below are no-ops.
     auto span = SpanGuard::childSpan(consensus::span::updatePositions, establishSpanContext_);
     span.setAttribute(
         consensus::span::attr::convergePercent, static_cast<int64_t>(convergePercent_));

include/xrpl/consensus/ConsensusSpanLabels.h

@@ -3,10 +3,11 @@
 /**
  * Enum-to-label mappings for consensus span attribute values.
  *
- *  Split from ConsensusSpanNames.h so that header stays dependency-free like
- *  its siblings: the span-name and attribute-key constants are included by
- *  overlay and app translation units that have no use for the consensus
- *  enums, while these mappings are needed only by Consensus.h.
+ *  These mappings live in their own header so ConsensusSpanNames.h stays
+ *  dependency-free like its siblings: the span-name and attribute-key
+ *  constants are included by overlay and app translation units that have no
+ *  use for the consensus enums, while these mappings are needed only by
+ *  Consensus.h.
  *
  *      ConsensusSpanNames.h  (constants only, no domain deps)
  *              ^