Add clip_release_device/clip_restore_device (and mtmd_release_device/
mtmd_restore_device wrappers over the vision + audio contexts) that free
the multimodal encoder's device weight buffer to a read-only host shadow
and rebuild it on demand, using the same shadow/free/reallocate pattern
as llama_model weights. No-op for a CPU-backed encoder. This lets the
server drop the ~hundreds-of-MiB vision encoder from VRAM when it is not
encoding an image.
Assisted-by: Claude
Lumpiasty
da76fcb326