Phase 1b: Telemetry core infrastructure

Add the OpenTelemetry telemetry library and supporting infrastructure:

Build system:
- Conan opentelemetry-cpp dependency with OTLP/gRPC exporter
- CMake integration for xrpl_telemetry library target
- Levelization ordering updates

Core library (libxrpl):
- Telemetry class: provider lifecycle, span creation, sampling config
- SpanGuard: RAII span management with attribute/exception helpers
- TelemetryConfig: parse [telemetry] config section
- NullTelemetry: no-op implementation when telemetry is disabled

Application integration:
- Telemetry member in ApplicationImp with start/stop lifecycle
- getTelemetry() interface on Application
- ServiceRegistry telemetry accessor

Docker observability stack:
- OTel Collector, Jaeger, Grafana docker-compose setup
- Collector config with OTLP gRPC receiver and Jaeger exporter

Config and docs:
- Example telemetry config section in xrpld-example.cfg
- Build documentation for telemetry setup

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

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

@@ -32,6 +32,8 @@ libxrpl.server > xrpl.server
 libxrpl.shamap > xrpl.basics
 libxrpl.shamap > xrpl.protocol
 libxrpl.shamap > xrpl.shamap
+libxrpl.telemetry > xrpl.basics
+libxrpl.telemetry > xrpl.telemetry
 libxrpl.tx > xrpl.basics
 libxrpl.tx > xrpl.conditions
 libxrpl.tx > xrpl.core
@@ -206,6 +208,7 @@ xrpl.server > xrpl.shamap
 xrpl.shamap > xrpl.basics
 xrpl.shamap > xrpl.nodestore
 xrpl.shamap > xrpl.protocol
+xrpl.telemetry > xrpl.basics
 xrpl.tx > xrpl.basics
 xrpl.tx > xrpl.core
 xrpl.tx > xrpl.ledger
@@ -224,6 +227,7 @@ xrpld.app > xrpl.rdb
 xrpld.app > xrpl.resource
 xrpld.app > xrpl.server
 xrpld.app > xrpl.shamap
+xrpld.app > xrpl.telemetry
 xrpld.app > xrpl.tx
 xrpld.consensus > xrpl.basics
 xrpld.consensus > xrpl.json