feat: add public C++ operator API

[voltjia]

Summary

• Add the unified public entry header include/infini/ops.h for C++ consumers.
• Generate public one-shot operator declarations under infini::ops::functional in generated/include/infini/functional_ops.h.
• Compile generated functional operator definitions into libinfiniops.
• Route pybind one-shot operator calls through infini::ops::functional::<OpName>.
• Install public headers, libinfiniops, pkg-config metadata, and CMake package metadata.

Motivation

This is the first PR in the public operator API split. It adds the C++ source/link convenience layer first so the later stable C ABI can be implemented as a thin adapter over public C++ operator entrypoints instead of including backend kernel headers directly.

Closes #N/A

Type of Change

• feat - new feature / new operator / new platform
• fix - bug fix
• perf - performance improvement (no behavioral change)
• refactor - code restructuring without behavior change
• test - adding or fixing tests only
• docs - documentation only
• build / ci - build system or CI configuration
• chore - tooling, formatting, or other non-code changes
• Breaking change (requires a ! in the Conventional Commits prefix or a BREAKING CHANGE: footer)

Platforms Affected

• CPU (WITH_CPU)
• NVIDIA (WITH_NVIDIA)
• Iluvatar (WITH_ILUVATAR)
• MetaX (WITH_METAX)
• Cambricon (WITH_CAMBRICON)
• Moore (WITH_MOORE)
• Ascend (WITH_ASCEND)
• PyTorch C++ bindings (WITH_TORCH)
• Build system / CMake / CI
• Python bindings / user-facing API

Test Results on Supported Platforms

Platform	Built	pytest Result	Notes / Hardware
NVIDIA	Yes	tests/test_cpp_api.py: 1 passed	Remote ssh nvidia, container accelerator-dev/nvidia:latest; build configured with WITH_CPU=ON, WITH_NVIDIA=ON.
Iluvatar	No	Not run	No Iluvatar hardware/toolchain available in this session.
MetaX	No	Not run	No MetaX hardware/toolchain available in this session.
Cambricon	No	Not run	No Cambricon hardware/toolchain available in this session.
Moore	No	Not run	No Moore hardware/toolchain available in this session.
Ascend	No	Not run	No Ascend hardware/toolchain available in this session.

Full `pytest` output (optional)

INFINIOPS_INSTALL_PREFIX=/workspace/project/.remote-install-pr1 python -m pytest tests/test_cpp_api.py -q
Running 1 items in this shard
.                                                                        [100%]
1 passed in 1.40s

Additional build checks on ssh nvidia with accelerator-dev/nvidia:latest:

cmake -S . -B .remote-build-pr1 -DWITH_CPU=ON -DWITH_NVIDIA=ON -DGENERATE_PYTHON_BINDINGS=OFF -DCMAKE_BUILD_TYPE=Release
cmake --build .remote-build-pr1 --target infiniops -j2
cmake --install .remote-build-pr1 --prefix .remote-install-pr1
cmake -S . -B .remote-build-pr1-pybind -DWITH_CPU=ON -DWITH_NVIDIA=ON -DGENERATE_PYTHON_BINDINGS=ON -DCMAKE_BUILD_TYPE=Release
cmake --build .remote-build-pr1-pybind --target ops -j2

Build emitted existing CUDA warnings around meaningless const return qualifiers and partially overridden overloads.

Benchmark / Performance Impact

N/A. This PR adds public API wrappers and build/install plumbing. It does not change operator kernels or dispatch selection.

Notes for Reviewers

• The C++ API is intentionally a source/link convenience layer, not a stable C++ ABI commitment.
• Public one-shot calls live in infini::ops::functional to avoid colliding with existing operator classes such as infini::ops::Add.
• Backend implementation headers remain in generated source files; the public header does not include backend kernel headers.
• The wrapper generator now has a constrained fallback parser for the current base operator headers when Python clang.cindex is unavailable in direct CMake builds.
• This PR should land before the C ABI PR. The follow-up C ABI PR should target this branch.

---

Checklist

Title, Branch, and Commits

• PR title follows Conventional Commits: feat: add public C++ operator API.
• Branch name follows the expected <type>/... form: feat/cpp-operator-api.
• Commit message follows Conventional Commits: feat: add public C++ operator API.
• Small PR is a single squashable commit.
• No stray merge commits from master.
• No fixup! / squash! / wip commits remain.

Scope and Design

• Changes are minimal for the stated motivation.
• No dead code, commented-out blocks, debug prints, or ownerless TODOs were added.
• No unrelated formatting churn was added.
• Public API changes are intentional and covered by smoke tests.

General Code Hygiene

• Comments were added only where they explain non-obvious behavior.
• Modified and added files end with a single trailing newline.
• git diff --check passed.
• Comments and error messages are in English.
• Comments and error messages are complete sentences where applicable.

C++ Specific

• Code follows the repository's Google C++ style conventions to the extent verified manually.
• clang-format version 21 was not run in this session; remote build and git diff --check passed.
• clang-tidy was not run in this session.
• Operator parameter order is preserved from the generated base operator signatures.
• No explicit exceptions are thrown by the added code.
• N/A - no kernel files or launchers were added.
• N/A - no new operator implementation classes were added.
• No raw new/delete was added by this PR.

Python Specific

• Python changes are limited to tests and generator code.
• ruff check / ruff format --check were not run in this session.
• Python smoke test passed remotely.

Testing

• Relevant remote NVIDIA build and pytest results are recorded above.
• Untested platforms are explicitly noted in the table.
• New public C++ API has a smoke test under tests/test_cpp_api.py.
• N/A - no new operator numerical tests were added.
• N/A - no bug-fix regression test is required.

Build, CI, and Tooling

• pip install .[dev] was not run.
• CMake configure/build/install paths were verified remotely.
• GENERATE_PYTHON_BINDINGS=ON pybind target still builds remotely.
• No new runtime dependency was added.

Documentation

• README-level public API documentation was not added in this PR.
• Public API surface is exposed through installed headers and covered by smoke tests.
• N/A - no user-visible breaking change is introduced.

Security and Safety

• No secrets, access tokens, internal URLs, customer data, or personal hardware identifiers were committed.
• No third-party code was added.
• No unsafe pointer arithmetic, uninitialized reads, or missing bounds checks were introduced.

[voltjia]

请列出几组通过这样暴露出的 API 的函数签名。