fix(telemetry): address code review findings for Phase 4 consensus tracing

Fix quorum attribute to use actual validator quorum instead of proposer
count, add missing ConsensusState::Expired handling in haveConsensus()
span, move ConsensusSpanNames.h to xrpld/consensus/ to resolve
levelization cycle, remove unused constants, enrich proposal receive
span with sequence, and correct stale documentation references.

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

.github/scripts/levelization/results/loops.txt

@@ -7,9 +7,6 @@ Loop: test.jtx test.unit_test
 Loop: xrpl.telemetry xrpld.rpc
   xrpld.rpc > xrpl.telemetry
 
-Loop: xrpld.app xrpld.consensus
-  xrpld.app > xrpld.consensus
-
 Loop: xrpld.app xrpld.overlay
   xrpld.app > xrpld.overlay
 

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

@@ -236,6 +236,7 @@ xrpl.tx > xrpl.protocol
 xrpld.app > test.unit_test
 xrpld.app > xrpl.basics
 xrpld.app > xrpl.core
+xrpld.app > xrpld.consensus
 xrpld.app > xrpld.core
 xrpld.app > xrpl.json
 xrpld.app > xrpl.ledger