[WIP] Add unit test framework with C++ (GoogleTest) and Python (pytest) test suites

[chenshengxin2026]

Summary

• Add 12 C++ GoogleTest tests covering runtime internals: task graph
  construction (host_build_graph), ring buffers (HeapRing, TaskRing),
  dependency pool, tensor overlap detection, TensorMap hash table,
  ReadyQueue (lock-free MPMC), shared memory layout, task state machine,
  scope mechanism, and handshake protocol macros
• Add 5 Python pytest tests covering build infrastructure: ELF/Mach-O
  parsing (elf_parser), toolchain flag generation (toolchain), kernel
  compilation pipeline (kernel_compiler), CMake-based runtime compilation
  (runtime_compiler), and ctypes bindings (bindings)
• Add CMake build system (tests/cpp/CMakeLists.txt) with GoogleTest
  auto-fetch fallback and stub library for host-side testing
• Update ci.sh to run both unit test suites before platform-specific
  integration tests, requiring no hardware or simulation environment

Motivation

The existing test infrastructure relies on end-to-end device tests or simulation
(ci.sh -p a2a3 / a2a3sim), which are slow and require specific environments. These
unit tests validate individual data structures and Python modules in isolation, enabling
faster development feedback loops and CI gating without hardware dependencies.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the project's testing infrastructure by integrating dedicated unit test frameworks for both C++ and Python components. This initiative aims to provide faster development feedback loops and enable more efficient continuous integration by validating individual modules in isolation, thereby reducing reliance on slower, environment-dependent end-to-end device tests.

Highlights

• C++ Unit Test Framework: Added a C++ unit test framework under 'tests/cpp/' utilizing GoogleTest and CMake, including a stub library to decouple tests from device-specific platform code.
• C++ Test Suites for Core Runtime Data Structures: Introduced four new C++ test suites for critical runtime data structures: 'HeapRing' (ring buffer allocator), 'PTO2ReadyQueue' (lock-free MPMC scheduler queue), 'Runtime' (task DAG in 'host_build_graph'), and 'TensorMapEntry' overlap detection.
• Python Unit Tests: Implemented Python unit tests under 'tests/unit/' using pytest to validate 'elf_parser.py' (ELF64/Mach-O binary parsing) and 'toolchain.py' (compiler toolchain configuration).

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[gemini-code-assist]

Code Review

This pull request introduces a comprehensive unit test framework for both C++ and Python components, which is a significant improvement for code quality and development velocity. The tests are well-structured and cover a wide range of scenarios, including core data structures, binary parsing, and toolchain configuration. My feedback focuses on a few areas to enhance maintainability and test robustness: improving the CMake helper function for consistency, cleaning up test code, and strengthening the logic in a concurrent stress test to ensure it's more effective.