POD's affine textured fan drawers measured and ported

REA with Ghidra confirmed the register and carry behavior of POD 2.8's draw_gradient_spans (FUN_00493070) and its ordinary and keyed row drawers. I ported the independent drawer paths to pod_render::span::gradient and measured 240 full-frame cases against the POD executable: 120 ordinary and 120 keyed. Every frame matched byte for byte, including aligned pairs, transparent keyed texels, negative steps and multiple triangles.

The changed pixels from one ordinary case and one keyed case. The image visualizes fixture write coverage; it is not a captured game frame.

Ordinary spans duplicate sampled shades over pixel pairs after alignment. Keyed spans sample each texel separately and preserve the destination for texel zero.

The new Rust tests replay all 240 complete frames. Formatting, pod-render tests, the Un-POD binary tests, the native release build and the WebAssembly compile pass. This ports the drawer primitives; it does not yet connect runtime face-kind and source-flag dispatch. The current app still routes textured faces through its perspective path, so the grey roof areas remain unexplained. A same-camera capture with source face flags is the next evidence needed. See the renderer notes and checklist.