If we get our predictions wrong, this can be used to
set a lower memory limit as a workaround. Recent multi-gpu
refactoring accidentally removed it, so this adds it back.
This change adds support for multiple concurrent requests, as well as
loading multiple models by spawning multiple runners. The default
settings are currently set at 1 concurrent request per model and only 1
loaded model at a time, but these can be adjusted by setting
OLLAMA_NUM_PARALLEL and OLLAMA_MAX_LOADED_MODELS.
