Moves Cell, Glyph, Style, Color, UnderlineStyle, CellCoord, CellSize,
DiffSpan, Attachment to pmacs-protocol::cell. CellGrid (borrowed-slice
render surface) and fn diff() (rendering helper) stay in src/cell.rs
since they're instance-side rendering machinery, not wire shapes.
src/cell.rs gains 'pub use pmacs_protocol::{Cell, Glyph, Style, ...};'
at the top so every existing internal import (crate::cell::Cell, etc.)
keeps resolving. The cell-module tests live alongside CellGrid + diff
and reference the re-exported types via 'use super::*' — same as
before; no test changes needed.
Lib gate: still green (no regressions, 1314 passing).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Levi Neuwirth