Major redesign of `Rect` internal storage and API cleanup, laying groundwork for v1.0.
### Added
- `Rect::new(x, y, width, height)` — primary constructor matching game framework convention
- `Rect::from_tl_size(Pos, Size)` — renamed from `Rect::new(Pos, Size)`
- `Rect::width_usize()` / `Rect::height_usize()` — for indexing use
- `Pos::cmp_row_major()` — y-primary comparison for grid iteration
- `impl Display for Size` — formats as `10×20`
- Type aliases: `Pos16`, `PosI` for positions, `Rect16`, `RectI` for rectangles
- Optional `serde` feature (`serde = ["dep:serde"]`)
- `cargo-semver-checks` in CI
- `Block` layout, which stores data in continuous fixed-size (`W x H`) blocks
- `AGENTS.md` — guidelines for LLM contributors
### Changed
- **`Rect` internal storage changed** from `(l, t, r, b)` to `(x, y, w, h)` — all fields are `T`
- `Rect::width()` and `Rect::height()` now return `T` (was `usize`)
- `Rect::from_ltrb_unchecked()` is no longer `unsafe` — uses `debug_assert!`
- Removed `T: Int` bound from `Pos` and `Rect` struct definitions (`C-STRUCT-BOUNDS`)
- `Rect::new(Pos, Size)` renamed to `Rect::from_tl_size(Pos, Size)`
- `Layout` has been split into 2 traits:
- `Layout` for iterating over positions, rectangles, and elements
- `Linear` for an (optional) optimization of linear-aligned data
- Layouts are now `&self` instead of static-only, allowing for dynamic dispatch
- License changed to `MIT OR Apache-2.0` (was `MIT`)
- Lint configuration aligned with rg: added `rust.nursery`, `must_use_candidate`, more
### Removed
- `unsafe` code from production codebase (`forbid(unsafe_code)`)
- `AsRef` / `AsMut` impls on `Pos` (depended on `unsafe` pointer casts)
- `Rect::iter_pos` and related methods; use the layout traits instead
- `.gemini/GEMINI.md` — replaced by `AGENTS.md`