Fix _storage_main terminate_on_parent_death not working on mac

[jonathan-eq]

Prior to this commit, the terminate_on_parent_death function was only usable on linux, due to it using the prctl command. This commit creates a new thread which polls the parent process, and signals terminate when it can no longer find the parent.

Issue
Resolves #8452

Approach
Short description of the approach

(Screenshot of new behavior in GUI if applicable)

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure unit tests pass locally after every commit (git rebase -i main --exec 'pytest tests/ert/unit_tests -n logical -m "not integration_test"')

When applicable

• When there are user facing changes: Updated documentation
• New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• Large PR: Prepare changes in small commits for more convenient review
• Bug fix: Add regression test for the bug
• Bug fix: Create Backport PR to latest release

[jonathan-eq]

@JHolba Will outsourcing the parent-proccess-"living-situation"-polling to a new thread cause issues? This is the best thing chatgpt and I came up with.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 17.64706% with 14 lines in your changes missing coverage. Please review.

Project coverage is 90.70%. Comparing base (97478fa) to head (8bc64be).
Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ert/services/_storage_main.py	17.64%	14 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9110   +/-   ##
=======================================
  Coverage   90.69%   90.70%           
=======================================
  Files         349      350    +1     
  Lines       21764    21787   +23     
=======================================
+ Hits        19738    19761   +23     
  Misses       2026     2026           

Flag	Coverage Δ
cli-tests	39.01% <0.00%> (+0.01%)	⬆️
gui-tests	71.66% <0.00%> (-0.03%)	⬇️
performance-tests	49.23% <0.00%> (-0.02%)	⬇️
unit-tests	79.54% <17.64%> (+0.01%)	⬆️

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