* server : use pytest-xdist for server tests
This commit adds pytest-xdist to the server tests. This is pytest
plugin that distributes test execution across multiple CPU cores.
Assisted-by: pi:llama.cpp/qwen3.8-27B
Refs: https://github.com/ggml-org/llama.cpp/pull/26734#issuecomment-5220707042
* remove server_base_port and BASE_PORT
* use worksteal and pytest builting tmp_path
* server : save serialized image chunks at the end of the llama state
* server : support multimodal slot state save/restore with packed payload
* server : refine image slot state serialization
* server : support media slot state and centralize media validation
* server : remove unnecessary comment
* server : remove defensive media checks and move the chunk type check to validate()
Daniel Bevenius