feat(thead): support T-Head PPU with NCCL

[spike-zhu]

Summary

Add T-Head PPU support to InfiniCCL through the NCCL-compatible library shipped in the T-Head CUDA SDK.

The change introduces the T-Head device/runtime abstraction, registers the device in the backend-device map, and extends the NCCL backend so existing collective APIs can operate on T-Head PPU memory.

Changes

• T-Head Backend
  Add T-Head backend support to InfiniCCL.
  Add T-Head device and runtime definitions.
  Add T-Head NCCL-compatible API interfaces.

• Device Management
  Add T-Head device implementation and data type support.
  Update backend-device mapping for the T-Head backend.

• Build System
  Update CMake configuration to build the T-Head backend.
  Add the required T-Head backend source files and headers.

Platform and Backend Affected

Platform

• CPU
• NVIDIA GPU
• Iluvatar GPU
• MetaX GPU
• Moore Threads GPU
• Cambricon MLU
• HYGON DCU
• T-Head PPU

Backend

• OpenMPI
• MPICH
• NCCL/RCCL
• MCCL

Performance Impact

• No performance impact
• Performance improved
• Performance regression possible

If applicable, provide benchmark results.

Known Issues & Future Work

Test Results

• Host: T-Head PPU node
• Device: 2 x T-Head PPU
• SDK: T-Head PPU CUDA SDK
• Backends tested: NCCL and OpenMPI+NCCL
• Build type: Release

Test Involved Platform

• CPU
• NVIDIA GPU
• Iluvatar GPU
• MetaX GPU
• Moore Threads GPU
• Cambricon MLU
• HYGON DCU
• T-Head PPU

Test Involved Backend

• OpenMPI
• MPICH
• NCCL/RCCL
• MCCL

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Checklist

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Title, Branch, and Commits

• PR title follows Conventional Commits (e.g. feat: …, fix(nccl): …).
• Branch name follows <type>/xxx-yyyy-zzzz where <type> matches the PR title's Conventional Commits type and words are joined with hyphens (see CONTRIBUTING.md §Branches).
• Each commit message follows Conventional Commits.
• Small PR is a single squashable commit; or, for a large PR, every commit is meaningful, well-formed, and independently reviewable (see CONTRIBUTING.md §Pull Requests).
• No stray merge commits from master — the branch is rebased cleanly on top of the current master.
• No fixup! / squash! / wip commits remain.

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.
• clang-format version 16 has been run against all applicable modified files; the diff is clean.
• No exceptions are thrown, and error paths use the required assertion pattern.
• Error and warning message wording follows the LLVM Coding Standards.
• Constructor initializer-list ordering is correct.
• Class, function, member, and namespace spacing follows the required formatting rules.

Python Specific (if Python files changed)

N/A. No Python source files are changed in this PR.
ruff check and ruff format --check were still run and passed.

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.

Security and Safety

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