feat: add graphical capabilities to core items and widgets

[forntoh]

Summary

• Add GraphicalMenuItem capability support across core items and widget-backed items, including graphical value-width measurement, toggle/list indicators, and a BasicItem implementation for ITEM_BASIC/ITEM_LABEL.
• Improve widget/item drawing safety for graphical rendering by hardening buffer handling (ITEM_DRAW_BUFFER_SIZE growth, null-safe bool widget formatting) and exposing optional GraphicalValueSelectionRenderer extension hooks.
• Add unit coverage for new item capabilities in test/ItemValue.cpp and document the new graphical item capability model in docs/source/overview/rendering/graphical-display.rst.

[coderabbitai]

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