Major change to the backend that allows for pluggable versions of llama.cpp/ggml. This was squashed merged from dlopen_backend_5 where the history is preserved.
Fix occurrences of the prompt callback being incorrectly specified, or
the response callback's prototype being incorrectly used in its place.
Signed-off-by: Juuso Alasuutari <juuso.alasuutari@gmail.com>