feat: support HYGON RCCL

[Ziminli]

Summary

This PR adds HYGON RCCL support by reusing InfiniCCL's existing NCCL backend. CMakeLists.txt detects HYGON RCCL headers and libraries from the DTK/ROCm environment, while src/backends/ccl/nccl/compat.h selects the NCCL-compatible vendor header. Device-specific datatype traits preserve the existing NVIDIA and Iluvatar behavior and add HYGON BF16 capability handling.

Changes

• Build and Dependency Detection

  • Detect HYGON RCCL through environment variables, standard /opt/dtk locations, and smi program;
  • Locate RCCL headers and libraries and propagate INFINI_CCL_USE_RCCL to the InfiniCCL library and examples.

• NCCL-family Backend Integration

  • Add conditional NCCL/RCCL header selection in src/backends/ccl/nccl/compat.h;
  • Add the HYGON CclApi specialization and enable the NCCL/HYGON backend combination;
  • Reuse the common NCCL collective implementation for RCCL.
  • Move BF16 mapping into NcclDataTypeTraits so support can vary by device platform;
  • Preserve NVIDIA and Iluvatar BF16 handling and use RCCL_BFLOAT16 for HYGON.

• Documentation Update

  • Update README.md and then PR template to show RCCL support.

Platform and Backend Affected

Platform

• CPU
• NVIDIA GPU
• Iluvatar GPU
• MetaX GPU
• Moore Threads GPU
• Cambricon MLU
• HYGON DCU

Backend

• OpenMPI
• MPICH
• NCCL
• MCCL

Performance Impact

• No performance impact
• Performance improved
• Performance regression possible

N/A. This PR adds RCCL backend support and does not change the collective algorithms or communication data path used by existing platforms.

Known Issues & Future Work

N/A.

Test Results

Test Involved Platform

• CPU
• NVIDIA GPU
• Iluvatar GPU
• MetaX GPU
• Moore Threads GPU
• Cambricon MLU
• HYGON DCU

Test Involved Backend

• OpenMPI
• MPICH
• NCCL
• MCCL

HYGON RCCL (single BW1000 node):
ccl_all_reduce.log

HYGON RCCL + OMPI (2 HYGON BW1000 nodes):
ccl_mpi_hybrid_all_reduce.log

Iluvatar NCCL + OMPI (single BI-150 node):
ccl_mpi_hybrid_all_reduce.log

NVIDIA NCCL + OMPI (single A100 node):
ccl_mpi_hybrid_all_reduce.log

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Checklist

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Title, Branch, and Commits

• PR title follows Conventional Commits (e.g. feat: …, fix(nccl): …).
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Scope and Design

• Changes are minimal — no unrelated modifications were introduced (CONTRIBUTING.md §Code/General).
• No dead code, commented-out blocks, debug prints, printf/std::cout/print(...) left behind, or TODO without an owner and issue link.
• No unrelated formatting churn that would obscure the diff.
• Public API changes (if any) are intentional, documented, and reflected in affected callers/tests.

General Code Hygiene

• The code is self-explanatory; comments were added only where the intent or rationale is non-obvious (CONTRIBUTING.md §Code/General).
• Every modified or added file ends with a single trailing newline (CONTRIBUTING.md §Code/General).
• No trailing whitespace, inconsistent indentation, or mixed formatting styles remain.
• Identifiers referenced in comments or error messages are wrapped in Markdown backticks (e.g. the `AllReduce` implementation) (CONTRIBUTING.md §Code/General).
• All comments and error messages are in English (CONTRIBUTING.md §Code/General).
• Comments and error messages are complete sentences — capitalized first letter, terminal punctuation — unless the language/framework convention says otherwise (CONTRIBUTING.md §Code/General; §Python).

C++ Specific (if C++ files changed)

• Code follows the Google C++ Style Guide strictly.
• clang-format (version 16, per .github/workflows/clang-format.yml) has been run against all modified applicable files; the diff is clean.
• No exceptions are thrown. Error paths use assert with messages that include at least __FILE__, __LINE__, and __func__ (CONTRIBUTING.md §C++).
• Error and warning message wording follows the LLVM Coding Standards (CONTRIBUTING.md §C++).
• Constructor initializer list order matches member declaration order (CONTRIBUTING.md §C++).
• Exactly one blank line between classes, between classes and functions, and between functions (CONTRIBUTING.md §C++).
• Exactly one blank line between members (functions and variables) within a class (CONTRIBUTING.md §C++).
• Exactly one blank line before and after the contents of a namespace (CONTRIBUTING.md §C++).

Python Specific (if Python files changed)

• N/A. No Python files are changed.

Testing

• All applicable example programs have been built and tested successfully on at least one supported heterogeneous cluster setup.

Build, CI, and Tooling

• New backends or devices have been added to auto-detection in CMakeLists.txt under if(AUTO_DETECT_DEVICES) or to if(AUTO_DETECT_BACKENDS) if applicable.
• Both CI workflows (clang-format.yml, ruff.yml) are green locally (or expected to be green on CI).

Documentation

• README.md, CONTRIBUTING.md, or inline docs updated when behavior, build flags, or developer workflow changed.
• N/A- Any user-visible breaking change is called out explicitly under "Summary" and in the commit/PR title with a ! or BREAKING CHANGE: footer.

Security and Safety

• No secrets, access tokens, internal URLs, customer data, or personal hardware identifiers have been committed.
• N/A- Third-party code is license-compatible and attributed.
• No unsafe pointer arithmetic, uninitialized reads, or missing bounds checks were introduced.