Vello renders image with a half-pixel offset

Drag an image into the viewport and view it at 100% scale. Toggle the Vello renderer on and off. Notice that it shifts down and left when Vello is active, and that it becomes blurry in the Vello version because anti-aliasing is applied to do the shifting. Also at slightly different from screenspace-aligned integer scales, we have the bottom and right edges wrap and appear as a 1px strip along the top and left edges.

https://github.com/user-attachments/assets/8e4a4916-61ca-49c5-aed5-062d72cbc271

My hypothesis is that between SVG and Vello, one assumes pixel coordinates are at the center of a pixel vs. the top left of the pixel.

Reproduce el problema arrastrando una imagen al viewport, visualizándola a una escala del 100% y alternando el renderizador Vello. Compara las rutas de renderizado de SVG y Vello, centrándote en las convenciones de coordenadas de píxel y en el comportamiento cerca de escalas enteras. Se considera terminado cuando la imagen permanece alineada y nítida, sin tiras de borde de 1px envueltas.

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