[SDK] Handle instrumentation object construction failures safely

[22elix3r]

Fixes #4361

Changes

Provider construction happens during SDK initialization. Runtime GetTracer / GetLogger / GetMeter calls must not throw. This change follows the post-SIG direction from @dbarker:

• Remove noexcept from the SDK constructors for TracerProvider, LoggerProvider, MeterProvider, Tracer, Logger, and Meter. Allocation or initialization failures during provider construction can now propagate so the caller (often the configuration library) can handle them.
• Keep GetTracer, GetLogger, and GetMeter noexcept. If constructing a previously unseen tracer/logger/meter fails, the provider catches the exception (when exceptions are enabled), logs via OTEL_INTERNAL_LOG_ERROR without letting logging escape, and returns a valid noop API object.
• The noop fallback is allocated during provider construction (new NoopTracer / NoopLogger / NoopMeter stored as a nostd::shared_ptr). Runtime failure handling does not allocate a fresh noop object.
• Failed construction is not inserted into the provider cache. A later Get* call can retry and return a normal SDK object once the failure is gone. Existing cached objects continue to be returned unchanged.
• The complete fallible path is protected: instrumentation-scope construction, configurator evaluation, object allocation, shared_ptr control-block allocation, cache insertion, and metrics AddMeter.
• Public API virtual method exception contracts are unchanged. ABI v1 and ABI v2 Get* signatures are unchanged. Try/catch is compiled only when OPENTELEMETRY_HAVE_EXCEPTIONS is set.

Tests added

• Constructor noexcept static_asserts for each signal.
• Deterministic fault injection through a ScopeConfigurator matcher that throws for a named scope.
• After failure, Get* returns a valid noop-compatible object, using it produces no telemetry, the cache is not poisoned, cached objects are unchanged, and a later call recovers when the injected failure is removed.
• Those tests are skipped when exceptions are disabled.

Validation

cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug \
  -DOTELCPP_WITH_EXAMPLES=OFF -DOTELCPP_BUILD_TESTING=ON \
  -DOTELCPP_WITH_OTLP_GRPC=OFF -DOTELCPP_WITH_OTLP_HTTP=OFF \
  -DOTELCPP_WITH_OTLP_FILE=OFF -DCMAKE_CXX_STANDARD=17

cmake --build build --target tracer_provider_test logger_provider_sdk_test meter_provider_sdk_test
ctest --test-dir build --output-on-failure \
  -R 'trace.(TracerProvider|TracerConfig)|logs.(LoggerProviderSDK|LoggerConfig)|metrics.(MeterProvider|MeterConfig)'
# 63/63 passed, including Get*ReturnsNoopOnConstructionFailure

ctest --test-dir build --output-on-failure -R 'logs.LoggerSDK'
# 12/12 passed

./build/sdk/test/metrics/meter_test
# 20/20 passed

# Exception-disabled compile of changed SDK sources:
g++ -std=c++17 -fno-exceptions -c -DOPENTELEMETRY_HAVE_EXCEPTIONS=0 ...
# tracer_provider.cc, tracer.cc, logger_provider.cc, logger.cc,
# meter_provider.cc, meter.cc: success

# ABI v2 compile of the three provider .cc files:
g++ -std=c++17 -c -DOPENTELEMETRY_ABI_VERSION_NO=2 ...
# tracer_provider.cc, logger_provider.cc, meter_provider.cc: success

git diff --check
# clean

tools/format.sh was not run: clang-format is not installed in this environment.

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed (SDK constructor exception specs only; API Get* contracts unchanged)

[codecov]

Codecov Report

❌ Patch coverage is 76.13636% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.59%. Comparing base (68a575f) to head (1271d6f).

Files with missing lines	Patch %	Lines
sdk/src/logs/logger_provider.cc	70.00%	9 Missing ⚠️
sdk/src/metrics/meter_provider.cc	76.93%	6 Missing ⚠️
sdk/src/trace/tracer_provider.cc	79.32%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4469      +/-   ##
==========================================
- Coverage   82.62%   82.59%   -0.03%     
==========================================
  Files         512      512              
  Lines       20139    20194      +55     
==========================================
+ Hits        16638    16677      +39     
- Misses       3501     3517      +16     

Files with missing lines	Coverage Δ
sdk/include/opentelemetry/sdk/metrics/meter.h	57.15% <ø> (ø)
sdk/include/opentelemetry/sdk/trace/tracer.h	100.00% <ø> (ø)
sdk/src/logs/logger.cc	94.12% <100.00%> (ø)
sdk/src/metrics/meter.cc	81.36% <100.00%> (ø)
sdk/src/trace/tracer.cc	80.22% <100.00%> (ø)
sdk/src/metrics/meter_provider.cc	85.51% <76.93%> (-6.80%)	⬇️
sdk/src/trace/tracer_provider.cc	83.96% <79.32%> (-4.75%)	⬇️
sdk/src/logs/logger_provider.cc	84.00% <70.00%> (-7.07%)	⬇️

... and 2 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.