feat: add benchmark suite for concurrent scans and report generation (#256)

[divyansha12]

Description

Implements a production-grade, offline-first performance benchmark suite to measure, baseline, and prevent regressions in critical SecuScan performance areas. This PR covers:

• Concurrent Task Creation: Throughput and P50/P95 latencies for task start operations.
• Parser & normalizer throughput: Performance checks for report payload construction and finding normalization.
• Database operations: Read latencies for fetching multiple rows and singular key lookups.
• Export execution: CSV and HTML rendering latency performance.
• SAT-3 slot saturation protection: Explicit resource safety test checking instantaneous reject times.
• CLI benchmark runner: A standalone comparison script (scripts/run_benchmarks.py) that checks measurements against thresholds.json.

No third-party pip dependencies were added, relying solely on standard library utilities (time, statistics) and existing dev-requirements (pytest, pytest-asyncio).

Related Issues

Closes #256

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?

• Benchmark Suite: Run locally with python3 scripts/run_benchmarks.py to confirm that all 11 performance metrics correctly query and pass against baseline thresholds.
• Existing Test Verification: Run ./testing/test_python.sh to ensure all 349 existing test cases pass and benchmarks are correctly excluded from the main test suite.
• Linting and Hygiene: Ran ruff check and git diff --check to ensure no trailing whitespace or lint warnings.

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.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.

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