Llama.cpp support

[tazarov]

Refs:

• https://github.com/go-skynet/go-llama.cpp
• https://pkg.go.dev/github.com/matthewrennie/go-llama.cpp

We're leaning more in the direction of https://github.com/matthewrennie/go-llama.cpp/blob/main/llama.go but with a dynamic path being set by the user or perhaps automatically (download to cached location).