fix: close HTTP response and file handles to prevent resource leaks

[lxcxjxhx]

Summary

Fix resource leaks by ensuring proper closure of HTTP responses and file handles using context managers.

Changes

• Use with open(...) context manager in coverage_test_collection.py to ensure file handle closure
• Use with urlopen(...) context manager in fuzz_introspector_page_gen.py to properly close HTTP responses

Impact

Prevents potential resource exhaustion from unclosed file handles and HTTP connections, especially in long-running processes.

Testing

Local environment limitations prevent full dynamic testing; relying on CI/CD automated tests for verification.

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I apologize for any inconvenience caused by this PR. I noticed these resource leaks while reviewing the codebase and wanted to contribute a fix. Please let me know if any changes are needed.

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