Bug report

Bug description:

Parent: #146102

https://gist.github.com/devdanzin/b022ff2d1304a4b2b8d3d8750abd8da5

pylifecycle.c: Multiple init/fini cleanup bugs

Summary

5 bugs in interpreter lifecycle:

1. new_interpreter (line 2534): return status bypasses switch-back after save_tstate detach → thread state corruption.
2. pycore_init_builtins (line 860): Direct return leaks bimod ref.
3. add_main_module (line 2762): bimod/loader refs leaked on PyDict_SetItemString failure.
4. finalize_clear_modules_dict (line 1685): Return value of PyObject_CallMethodNoArgs never DECREF'd.
5. init_sys_streams (line 3019-3031): Unchecked PySys_SetObject for stdin/stdout (stderr correctly checked).

CPython versions tested on:

CPython main branch, 3.15

Operating systems tested on:

No response

Linked PRs

• gh-149630: Fix pylifecycle multiple init/fini cleanup bugs  #149631