fix(telemetry): fix CI failures — clang-tidy, levelization, linker

Clang-tidy fixes:
- Concatenate nested namespaces (modernize-concat-nested-namespaces)
  in OTelCollector.h, OTelCollector.cpp, ValidationTracker.h/.cpp
- Add missing direct includes (misc-include-cleaner) in
  ValidationTracker.cpp, test, CollectorManager.cpp, OTelCollector.cpp
- Make lock_guard variables const (misc-const-correctness)
- Add braces around single-line if/else (readability-braces-around-statements)
- Use designated initializer for WindowEvent (modernize-use-designated-initializers)
- Initialize LedgerEvent::seq field (cppcoreguidelines-pro-type-member-init)

Linker fix:
- Add ValidationTracker.cpp as source to xrpl.test.telemetry target
  (it lives in src/xrpld/ but the test links against libxrpl only)

Levelization fix:
- Remove stale dependency edges from ordering.txt that were introduced
  by the erroneous develop-merge commit

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

include/xrpl/beast/insight/OTelCollector.h

@@ -40,8 +40,7 @@
 #include <memory>
 #include <string>
 
-namespace beast {
-namespace insight {
+namespace beast::insight {
 
 /**
  * @brief A Collector that exports metrics via OpenTelemetry OTLP/HTTP.
@@ -88,5 +87,4 @@ public:
         Journal journal);
 };
 
-}  // namespace insight
-}  // namespace beast
+}  // namespace beast::insight