Plot operations implementations
Single Responsibility: Handle all plot creation and data addition operations including line plots, contours, surfaces, pcolormesh, scatter, histograms, boxplots, and specialized plots. Extracted from fortplot_figure_core_impl to maintain file size compliance.
── Initialization ────────────────────────────────────────────────
── Basic plot operations ─────────────────────────────────────────
── Specialized plot operations ───────────────────────────────────