refactor(mcp23009e): Migrate menu_navigation example to steami_screen.

[MatteoCnda1]

Summary

Migrate lib/mcp23009e/examples/menu_navigation.py from direct SSD1327 calls to the steami_screen widget API. Closes #374

Changes

• Replaced manual display.text() and hand-coded positioning with screen.menu(), screen.title(), screen.value() and screen.subtitle()
• Replaced ssd1327 direct instantiation with SSD1327Display + Screen wrapper
• Added @micropython.native decorator on is_any_pressed() for better performance in the button polling loop
• Extracted is_any_pressed() as a reusable helper function
• Removed manual layout constants (X0, TITLE_Y, ITEM_Y, etc.) — layout is now handled by steami_screen

Checklist

• ruff check passes
• python -m pytest tests/ -k mock -v passes (no mock test broken)
• Tested on hardware (STM32WB55 / STeaMi board)
• README updated (if adding/changing public API) — N/A, example only
• Examples added/updated (lib/mcp23009e/examples/menu_navigation.py)
• Commit messages follow <scope>: <Description.> format