Backport #402: Replace `exec_program` with `execute_process`

[azeey]

🦟 Bug fix

Fixes https://github.com/gazebosim/gz-plugin/issues/144

Summary

Backports #402 with an additional fix in fb831869b0dc06a1d937ac1e63f044f310111130

Checklist

• [ ] Signed all commits for DCO
• [ ] Added tests
• [ ] Updated documentation (as needed)
• [ ] Updated migration guide (as needed)
• [ ] Consider updating Python bindings (if the library has them)
• [ ] codecheck passed (See contributing)
• [ ] All tests passed (See test coverage)
• [ ] While waiting for a review on your PR, please help review another open pull request to support the maintainers

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