Fix Python 3.13 destructor error

[allburov]

Summary

• avoid OSError: Bad file descriptor when ApiClient is garbage collected
• revert to simple try/except for closing the pool
• remove extra cleanup tests

Testing

git clone https://github.com/devopshq/teamcity.git
cd teamcity
git checkout codex/fix-oserror-when-exiting-script-after-python-3.13-upgrade
pip install .

fix #59

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https://chatgpt.com/codex/tasks/task_e_68464a7f84948330b7b1379e8cfb85b5

[allburov]

Hi! @dvirtz could you test this solution for #59 🙏

[dvirtz]

I don't see error now. Thanks @allburov