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>

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

@@ -191,18 +191,12 @@ test.toplevel > xrpl.json
 test.unit_test > xrpl.basics
 test.unit_test > xrpl.protocol
 tests.libxrpl > xrpl.basics
-tests.libxrpl > xrpl.core
 tests.libxrpl > xrpld.telemetry
 tests.libxrpl > xrpl.json
-tests.libxrpl > xrpl.ledger
 tests.libxrpl > xrpl.net
-tests.libxrpl > xrpl.nodestore
 tests.libxrpl > xrpl.protocol
 tests.libxrpl > xrpl.protocol_autogen
-tests.libxrpl > xrpl.server
-tests.libxrpl > xrpl.shamap
 tests.libxrpl > xrpl.telemetry
-tests.libxrpl > xrpl.tx
 xrpl.conditions > xrpl.basics
 xrpl.conditions > xrpl.protocol
 xrpl.core > xrpl.basics