Cherry-picked upstream PR #522 (da4d3b5) with conflict resolution:
- Added new lib/hal/ files (HalDisplay, HalGPIO)
- Updated GfxRenderer to use HalDisplay, preserving base viewable margins
- Adopted PR #522's MappedInputManager lookup table implementation
- Updated main.cpp to use HAL while preserving custom Serial initialization
- Updated all EInkDisplay::RefreshMode references to HalDisplay::RefreshMode
This introduces a Hardware Abstraction Layer for display and GPIO,
enabling easier emulation and testing.
