Refactor: move RTLD_GLOBAL SO preload + simpler_log_init from C++ ChipWorker::init to Python

[ChaoWao]

Summary

Continues the API-narrowing theme of #723 / #735. ChipWorker::init was the last place in C++ doing process-wide SO bootstrap (dlopen libsimpler_log.so + on sim libcpu_sim_context.so with RTLD_GLOBAL, plus calling simpler_log_init to seed HostLogger). That moves up into the Python ChipWorker wrapper, shrinking the C++ init signature from 8 args to 4:

- void init(host_lib, aicpu, aicore, simpler_log_lib, device_id, sim_context_lib = "", log_level = 1, log_info_v = 5);
+ void init(host_lib, aicpu, aicore, device_id);

Why it's safe

_task_interface.so has no undefined HostLogger / unified_log_* symbols — chip_worker.cpp reaches host_runtime.so purely via dlsym, and the binding code doesn't log. So the RTLD_GLOBAL preload only has to precede the _ChipWorker.init dlopen of host_runtime.so, not module import. The Python wrapper does:

1. ctypes.CDLL(bins.simpler_log_path, mode=RTLD_GLOBAL) — once per process
2. <handle>.simpler_log_init(log_level, log_info_v) — seed HostLogger
3. on sim: ctypes.CDLL(bins.sim_context_path, mode=RTLD_GLOBAL)
4. self._impl.init(host_path, aicpu_path, aicore_path, device_id)

A module-level _preloaded_globals: dict[str, ctypes.CDLL] makes the loads idempotent per path (Python counterpart of the old std::once_flag). The ChipWorker.init wrapper's public signature (device_id, bins, log_level=None, log_info_v=None) is unchanged, so no caller updates.

Changes

• src/common/worker/chip_worker.{h,cpp} — drop the 4 init params; remove the g_simpler_log_* / g_sim_context_* globals, ensure_*_loaded() helpers, SimplerLogInitFn typedef + simpler_log_init_fn_ member, the simpler_log_init call, and the now-unused <mutex> include.
• python/bindings/task_interface.cpp — _ChipWorker.init def is now 4 args.
• python/simpler/task_interface.py — _preloaded_globals registry + _preload_global(); ChipWorker.init does the preload + simpler_log_init via ctypes, then the 4-arg _impl.init.
• tests/ut/py/test_chip_worker.py — the three _ChipWorker.init(...) fault-path tests drop the /nonexistent/libsimpler_log.so arg.
• Docs (chip-level-arch, dynamic-linking, logging, python/simpler/__init__.py, python/simpler/_log.py) — init-flow ASCII art / load-order / config-flow table now show the preload in the Python wrapper.

Testing

• pip install --no-build-isolation -e . (all 4 host_runtime.so + libsimpler_log compile)
• pytest tests/ut/py — 119 passed, 7 skipped (torch-missing tests excluded as before)
• examples/workers/l2/{hello_worker, worker_malloc} on a2a3sim and a5sim
• Onboard ut + st (runs in CI on Linux)

[gemini-code-assist]

Code Review

This pull request refactors the library preloading and logging initialization logic, moving the responsibility from the C++ ChipWorker implementation to the Python task_interface wrapper. The Python layer now uses ctypes.CDLL with RTLD_GLOBAL to load libsimpler_log.so and libcpu_sim_context.so (on simulation platforms) and seeds the HostLogger before calling the simplified C++ init method. Feedback suggests improving the robustness of the ctypes implementation by using RTLD_NOW for immediate symbol resolution, explicitly defining argtypes and restype for the C functions, and adding validation for mandatory library paths.