The profile slug in a model name, `profile:model`, is specific to
llama-swap. This strips `profile:` out of the model name request so
upstreams that expect just `model` work and do not require knowing about
the profile slug.
Switch from using a naive strings.Fields() to shlex.Split() for parsing the model startup command into a string[]. This makes parsing much more reliable around newlines, quotes, etc.
