chore: add a pure C worker example

[jfonseca-aneo]

Motivation

The ArmoniK C++ SDK already provides a worker wrapper in C++. This adds a sample showing how to write a worker usingthe lower-level C ABI (ArmoniKSDKInterface.h) directly, without the C++ SDK worker wrapper. This is useful for users who want to implement workers in pure C or in any language that can expose a C-compatible shared library.

Description

Adds a new cpp/HelloWorldC sample. The worker is a pure C shared library that implements the five armonik_*
functions from ArmoniKSDKInterface.h:

• armonik_create_service / armonik_destroy_service
• armonik_enter_session / armonik_leave_session
• armonik_call — dispatches on function_name to demonstrate three behaviors:
  • hello: appends " World!" to the payload and returns ARMONIK_STATUS_OK
  • error: returns ARMONIK_STATUS_ERROR (permanent task failure, no retry)
  • retry: returns ARMONIK_STATUS_RETRY (transient failure, ArmoniK reschedules up to max_retries)

The client is written in C++ using the existing ArmoniK C++ SDK and selects the behavior via --error / --retry
CLI flags.

Testing

Tested end-to-end against a local ArmoniK deployment with a cppdynamic partition:

• Normal mode (hello): task completes successfully, result is "Hello, World!".
• Error mode (--error): task fails permanently with TASK_STATUS_ERROR: Permanent error requested by client.
• Retry mode (--retry): task is retried three times (max_retries=3) then fails with the transient error
  message.

Expected outputs for all three modes are documented in the README.

Impact

• Adds a new standalone sample; no existing samples are modified.
• No new runtime dependencies: the C worker links only against libc at runtime — ArmoniKSDKInterface.h is the only compile-time dependency.
• No CI changes required (the existing C++ pipeline covers this sample).

Additional Information

• The worker .so filename must not include an SDK version suffix (unlike C++ SDK workers), because the dynamic
  worker loads it by the exact name passed in TaskOptions.

Checklist

• My code adheres to the coding and style guidelines of the project.
• I have performed a self-review of my code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• I have thoroughly tested my modifications and added tests when necessary.
• Tests pass locally and in the CI.
• I have assessed the performance impact of my modifications.

[aneojgurhem]

note: change it when release is available