rasterization of `shape` to `label` (e.g., polygons to mask)

[HelenaLC]

self-explanatory... for inspiration, see

• https://github.com/BiocCodingCollaborations/VeniceHackathon2026/blob/main/segmentation-analysis/R/shapes_to_labels.R
• https://github.com/BiocCodingCollaborations/VeniceHackathon2026/blob/main/segmentation-analysis/quarto/compute-by-polygon.qmd