Fix code review finding: use to_string for ConsensusMode attr

Replace hand-rolled ternary that missed switchedLedger with
existing to_string(ConsensusMode) which handles all 4 enum values.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: pratikmankawde

src/xrpld/app/consensus/RCLConsensus.cpp

@@ -282,11 +282,7 @@ RCLConsensus::Adaptor::onClose(
     XRPL_TRACE_CONSENSUS(app_.getTelemetry(), "consensus.ledger_close");
     XRPL_TRACE_SET_ATTR(
         "xrpl.consensus.ledger.seq", static_cast<int64_t>(ledger.ledger_->header().seq + 1));
-    XRPL_TRACE_SET_ATTR(
-        "xrpl.consensus.mode",
-        (mode == ConsensusMode::proposing
-             ? "proposing"
-             : (mode == ConsensusMode::observing ? "observing" : "wrongLedger")));
+    XRPL_TRACE_SET_ATTR("xrpl.consensus.mode", to_string(mode).c_str());
 
     bool const wrongLCL = mode == ConsensusMode::wrongLedger;
     bool const proposing = mode == ConsensusMode::proposing;