refactor: eliminate duplicates, fix constant magic numbers, simplify code
- Extract align_partial_region() helper to unify byte-alignment logic in
ssd1677 partial/full refresh paths.
- Collapse write_full_frame_async to delegate to write_full_frame.
- Extract read_averaged!() macro for 3x duplicate ADC oversampling.
- Add byte_to_char() helper to consolidate (0x20..=0x7E) patterns.
- Add FONT_SIZE_NAMES constant to unify Small/Medium/Large mappings.
- Fix sync_quick_menu to use reader::QA_FONT_SIZE instead of magic 1.
- Simplify ButtonMapper, collapse nested ifs, use div_ceil.
- Net: -59 lines, zero clippy warnings in pulp-os.