feat: add HYGON platform support across runtime, device, build, and launcher stack

[Ziminli]

Summary

This PR adds support for the HYGON platform, enabling both build-time and runtime integration. Existing examples using the MPI backends (e.g., OpenMPI) can now run on HYGON hardware with platform-specific specializations.

Changes include build logic, device priority handling, runtime specialization, and example execution support.

Changes

• Hygon Build Integration

  • Detects DTK through DTKROOT, DTK_ROOT, ROCM_PATH, HIP_PATH, or the default /opt/dtk path;
  • Finds DTK HIP headers, libamdhip64, and hipcc, then uses DTK hipcc as the C++ compiler for Hygon builds.

• Hygon Runtime Device Support

  • Adds Device::Type::kHygon, string mappings, and device priority handling in src/device.h;
  • Adds HIP-backed runtime wrappers in src/devices/hygon/runtime_.h;
  • Adds Hygon memory-space detection in src/devices/hygon/device_.h.

• Hygon Data Type and Casting Support

  • Maps InfiniCCL float16/bfloat16 types to DTK HIP half and hip_bfloat16 in src/devices/hygon/data_type_.h;
  • Adds Hygon hardware cast specializations in src/devices/hygon/caster_.h;
  • Forces Hygon half/bfloat16 MPI reductions through the existing float bridge path because DTK host staging buffers cannot rely on direct compound operators for these types.

• MPI Example Build Cleanup

  • Adds explicit return statements in small void helpers that DTK hipcc warned about. Touches:
    • src/communicator.h
    • src/backends/mpi/ompi/comm_instance.h, and
    • examples/utils.h.

• Documentation and Template Updates

  • Updated .github/pull_request_template.md to include HYGON as a supported platform;
  • Updated README.md to include HYGON as a supported platform.

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.

Known Issues & Future Work

• Hygon support is currently validated for MPI examples through OpenMPI only. RCCL/CCL integration is not implemented in this PR.
• When CUDA-compatible APIs and environment variables are enabled, setting AUTO_DETECT_DEVICES=ON will also detect and enable nvidia, which may cause errors at this point. In this case, it is recommended to disable AUTO_DETECT_DEVICES and manually enable only HYGON.

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 (single node, OpenMPI):
mpi_all_gather.log
mpi_all_reduce.log
mpi_all_to_all.log
mpi_broadcast.log
mpi_gather.log
mpi_reduce.log
mpi_reduce_scatter.log
mpi_scatter.log
mpi_send_recv.log

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Checklist

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Title, Branch, and Commits

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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 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.
• 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.