Performance benchmarks: validate 10-15x tool execution speedup

Description

Implement performance benchmarking suite to validate multi-threaded execution speedup claims (10-15x).

Scope

• Benchmark serial vs parallel tool execution
• Measure ThreadPoolExecutor efficiency (16 workers for tools, 32 for ports/DNS)
• Test against 10, 50, 100+ targets
• Measure email credential testing parallelization (8 workers)
• Profile memory usage under parallel execution
• Compare single-threaded vs multi-threaded execution time

Requirements

• Create benchmarking suite: tests/benchmarks/
• Compare execution times
• Generate performance report
• Track metrics over time (CI integration)
• Set performance regression thresholds

Files to Create

• tests/benchmarks/benchmark_execution.py
• tests/benchmarks/benchmark_dns_resolution.py
• tests/benchmarks/benchmark_email_auth.py
• perf_results.json (historical tracking)

Success Criteria

• Tool execution speedup: 8-15x with 16 workers
• Email auth speedup: 5-8x with 8 workers
• DNS/port scan speedup: 20-32x with 32 workers
• Memory usage < 500MB under concurrent execution
• Performance regression detection in CI

Start by locating the existing serial and threaded execution paths for tools, DNS/ports, and email authentication, then use them to populate tests/benchmarks/benchmark_execution.py, benchmark_dns_resolution.py, and benchmark_email_auth.py. Run the benchmarks against the listed target sizes, record perf_results.json, and verify the reported speedups, memory limit, and CI regression thresholds.