Added optional OpenTelemetry tracing for RPC loader calls

[Codingisinmyblud]

Description

Added optional OpenTelemetry tracing for the RPC loader to improve observability across distributed systems paths.

When built with -DOPTION_RPC_TRACING=ON, the RPC loader wraps both synchronous (function_rpc_interface_invoke) and asynchronous (function_rpc_interface_await) calls in an OpenTelemetry rpc_trace_scope. This emits spans that capture function name, target URLs, latency and also the success/failure resolution. I used a simple C++ RAII abstraction. When disabled (this is the default), a no-op implementation is linked which means there is absolute zero runtime overhead.

Dependencies added:

• OpenTelemetry C++ SDK (I believe this is fetched automatically via CMake FetchContent when the tracing is enabled)

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests/screenshots (if any) that prove my fix is effective or that my feature works.
• I have tested the tests implicated (if any) by my own code and they pass (make test or ctest -VV -R <test-name>).
• If my change is significant or breaking, I have passed all tests with ./docker-compose.sh test &> output and attached the output.
• I have tested my code with OPTION_BUILD_ADDRESS_SANITIZER or ./docker-compose.sh test-address-sanitizer &> output and OPTION_TEST_MEMORYCHECK.
• I have tested my code with OPTION_BUILD_THREAD_SANITIZER or ./docker-compose.sh test-thread-sanitizer &> output.
• I have tested with Helgrind in case my code works with threading.
• I have run make clang-format in order to format my code and my code follows the style guidelines.

If you are unclear about any of the above checks, have a look at our documentation here.

[viferga]

can you explain what are you tracing and how does it work? send a screenshot of it working in a telemetry environment

[Codingisinmyblud]

Hi, hope you're doing well.
In this PR I added the feature to trace both synchronous and asynchronous calls.

• For synchronous calls it captures the full lifecycle from serialization through the blocking HTTP POST and then finally to deserialization.
• For asynchronous calls, it captures the initial dispatch phase, which includes serialization and queueing.

With regards to how it works, I added a C++ RAII abstraction that manages the OpenTelemetry span lifecycle. It automatically extracts the target URL and method names to attach as standard attributes (rpc.method, metacall.target, metacall.async). If a network or serialization error were to occur, the span would securely be marked with the error status before destruction. When the OPTION_RPC_TRACING CMake flag is disabled, this class uses a strictly no-op backend, meaning there is zero runtime overhead.

The backend currently uses the built-in console exporter (OStreamSpanExporter). Standard out acts as the telemetry environment for now. I did this just to keep the PR simple and to prove that the architecture and attribute extraction work perfectly. We can easily swap to a OTLPSpanExporter for Zipkin or Jaeger in the fture.

I have attached a screenshot of the structured JSON synchronus call span and the asynchronus call span (from running the native test suite ctest -V -R metacall-rpc-test > test_output.txt)

For synchronous calls:

• 

For asynchronous calls:

• 

[viferga]

@Codingisinmyblud It looks great but I cannot merge it yet, I think we should discuss better how is the format and data we will use for tracing it. But it's a good start. For example I think we should serialize the body of the rpc call, so we know exactly how a function was called.

Also the variable for enabling this should be:

OPTION_BUILD_LOADERS_RPC_TELEMETRY

Maybe, or *_TRACING.

[Codingisinmyblud]

Sounds good. I'll get started on those changes for now. Thanks

[viferga]

The CI is failing, I cannot merge it if it doesn't compile.