🛡️ Sentinel: [MEDIUM] Fix File Descriptor Leakage in subprocess

[ManupaKDU]

🚨 Severity: MEDIUM
💡 Vulnerability: File Descriptor Leakage (CWE-403). Using subprocess.call with close_fds=False inside a multi-threaded ThreadPoolExecutor causes the newly spawned child process to inherit all file descriptors currently opened by any thread at the time of execution.
🎯 Impact: This can expose sensitive resources (e.g., open network sockets, secure files, or database connections) to the unprivileged child process or to attackers if the child process is compromised.
🔧 Fix: Replaced the micro-optimization close_fds=False with the secure default close_fds=True, ensuring a clean file descriptor table for the child process.
✅ Verification: Ensure tests pass via python3 -m unittest test_testping1.py and that bandit issues no new high severity warnings.

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PR created automatically by Jules for task 14717591058926584160 started by @ManupaKDU

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