[BENCHMARKING] CPU vs GPU comparison plots

[hubertwojcik]

Goal

Generate publication-quality plots from benchmark CSV data comparing all implementations across key dimensions.

Tasks

• Write scripts/plot_results.py using matplotlib
• Plot 1: throughput (GB/s) per implementation — bar chart
• Plot 2: OpenMP/MPI speedup vs thread/process count — line chart
• Plot 3: throughput vs pattern count — all implementations on one chart
• Plot 4: throughput vs text size — all implementations on one chart
• Save plots to benchmarks/plots/ as PNG + PDF

Acceptance Criteria

• All four plots generated from results.csv with a single python3 scripts/plot_results.py call
• Plots are legible with axis labels, legends, and titles
• Plots committed to benchmarks/plots/