Enhanced benchmarking task for Raxol terminal emulator.

Usage: mix raxol.bench # Run all benchmarks mix raxol.bench parser # Run parser benchmarks only mix raxol.bench terminal # Run terminal benchmarks only mix raxol.bench rendering # Run rendering benchmarks only mix raxol.bench memory # Run memory benchmarks only mix raxol.bench --quick # Quick benchmark run mix raxol.bench --compare # Compare with previous results mix raxol.bench --dashboard # Generate full dashboard mix raxol.bench --regression # Check for performance regressions