Feat/chaos tests issue 259

[divyansha12]

Adds comprehensive integration-level chaos tests to cover task execution failure modes, ensuring robust handling and recovery. Specifically:

1. Process crash during task execution: Simulates backend command execution failure and verifies the task/report states are marked as failed rather than staying stuck in running or pending.
2. Upsert failure after successful scan: Simulates a database failure during the final state update to verify the task is successfully marked as failed.
3. Non-zero exit but raw artifact present: Verifies that when a scanner exit status is non-zero, the task/report states are marked failed but the raw artifact file is still written to disk to aid debugging.
4. Concurrency slot release: Verifies that the task queue slot concurrency limiter is unconditionally released in a finally block even when a crash occurs, preventing queue starvation.

Additionally, this PR:

• Replaced hardcoded python3 command in test_python.sh with a checker to automatically find Python 3.11+ and reconstruct venv_tests if the version is outdated.
• Cleaned up auto-generated Playwright/test-results folders from git tracking and added them to .gitignore to comply with the project guidelines.
• Recalculated integrity checksums for all 60 plugins.

Related Issues

Closes #259

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

1. Ran all four new chaos integration tests: pytest -v testing/backend/integration/test_chaos_execution.py (all passed successfully).
2. Ran the full backend test suite: ./testing/test_python.sh (all 335 tests passed successfully).
3. Ran pre-commit run --all-files which fully succeeded across all hooks (including black, end-of-file-fixer, trailing-whitespace, and check-yaml).

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• My changes generate no new warnings.

🟢 GSSoC note – I’m a GSSoC contributor. All checks are passing; please add the gssoc:approved label when merging.