fix(telemetry): keep libxrpl SpanGuard test free of xrpld headers

The xrpl_tests target links only xrpl.libxrpl and cannot include the
xrpld-level ConsensusSpanNames.h / RpcSpanNames.h (CI build failure on
ubuntu-gcc-debug-arm64). Revert the test to underscore-form attribute
literals, restore the SpanNames.h include for seg::consensus, and drop
the now-unused tests.libxrpl -> xrpld.* levelization entries.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -207,8 +207,6 @@ test.unit_test > xrpl.protocol
 tests.libxrpl > xrpl.basics
 tests.libxrpl > xrpl.config
 tests.libxrpl > xrpl.core
-tests.libxrpl > xrpld.consensus
-tests.libxrpl > xrpld.rpc
 tests.libxrpl > xrpl.json
 tests.libxrpl > xrpl.ledger
 tests.libxrpl > xrpl.net