at_jl_exit sometimes crashes #764

Affects: JuliaCall

Describe the bug
When running multithreaded julia, python sometimes causes segmentation fault at exit.

Your system
Please provide detailed information about your system:

• Ubuntu 25.10
• Julia 1.12.6, Python 3.14.4, PythonCall 0.9.31, JuliaCall 0.9.31

Additional context

jl_atexit_hook(0) does three things in sequence:

1. Run user atexit hooks (Base._atexit(0)).
2. Schedule + run ALL registered finalizers (jl_gc_run_all_finalizers).
3. Tear down threads, set jl_gc_disable_counter = 1.

Finalizers are best-effort, and running them during shutdown with multiple threads is probably where the crashes come from. Since the process is exiting, the finalizers don't semantically need to run — they're unsafe and not useful.
I tested that with only Base._atexit(0), my custom julia atexit` lambdas are executed

Fixed by #763