[adkinsrs]

This pull request adds efficient image downsampling to the spatial viewer, reducing the amount of image data sent to the browser and improving performance, especially for large images. It also simplifies how dimmed background images are handled by sharing a single image source across plots and applying opacity at the renderer level, rather than creating separate copies. Additionally, the pull request increases the maximum wait time for tile rendering in the frontend.

Image downsampling and performance improvements:

• Added a downsample_image utility in services/spatial/common.py to shrink images so their longest side does not exceed a configurable maximum, reducing payload size sent to the browser. This is used when loading and updating images in the spatial viewer. [1] [2] [3] [4]
• Introduced MAX_DISPLAY_IMAGE_DIM class variable in BaseSpatialViewer and set it to a lower value (2000) in CondensedSpatialViewer, allowing different resolutions for different viewer types. [1] [2]

Dimmed image handling simplification:

• Removed the _build_dimmed_array method and now apply dimming using the renderer's global_alpha property, sharing a single image array across all plots to avoid redundant image copies and reduce memory usage. [1] [2] [3]

Frontend rendering adjustment:

• Increased the maximum polling wait time for tile rendering in www/js/classes/tilegrid.js from 1 minute to 3 minutes to better accommodate slow renders.