security: fix critical vulnerabilities found in code review

[Rehan018]

• Fix CWE-94 code injection in magic_commands.py by adding input validation and blocking dangerous shell commands in %% magic command handler
• Fix inadequate error handling in oi-mac-installer.sh by adding proper error handling for xcode-select --install command
• Fix CWE-400,664 resource leak in test_interpreter.py by ensuring proper cleanup of server processes in try-finally block

These fixes address critical security vulnerabilities that could allow arbitrary code execution and resource leaks that could impact system stability.

Describe the changes you have made:

Reference any relevant issues (e.g. "Fixes #000"):

Pre-Submission Checklist (optional but appreciated):

• [ ] I have included relevant documentation updates (stored in /docs)
• [ ] I have read docs/CONTRIBUTING.md
• [ ] I have read docs/ROADMAP.md

OS Tests (optional but appreciated):

• [ ] Tested on Windows
• [ ] Tested on MacOS
• [ ] Tested on Linux