at_jl_exit sometimes crashes

**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 https://github.com/JuliaPy/PythonCall.jl/pull/763

Review jl_atexit_hook(0), Base._atexit(0), and jl_gc_run_all_finalizers to understand the shutdown sequence described in the report. Compare the behavior and available tests with the fix in PythonCall.jl pull request 763; this issue is already marked as fixed there.

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