Configuration

WORKERS env variable: set total number of actix workers that will be handling client requests. This value should not be higher than the number of logical processors on the machine (https://actix.rs/docs/server/#multi-threading). 0 = number of logical processors.
VIPS_CONCURRENCY env variable: number of worker threads for libvips (https://www.libvips.org/API/current/VipsOperation.html#vips-concurrency-set); 0 = number of logical processors.

Minor fixes and improvements

Trying to lower memory usage by calling image_set_kill on VipsImage
Increased AVIF effort from 0 to 1 to make the performance match WEBP more closely and increase image fidelity while decreasing the output image size
Scheduled cache cleaning now runs every day at 1 AM