ggml : improve CI + add more tests

The current state of the testing framework is pretty bad - we have a few simple test tools in tests, but these are not maintained properly and are quite rudimentary. Additionally, the Github Actions do not allow to run heavy workloads so it is difficult to run integration tests even on small models such as GPT-2. Not to mention that there is no GPU support

Ideally, it would be awesome to make a CI that can build the code on as much different hardware as possible and perform some performance and accuracy tests for various models. This will allow quicker iteration over new changes to the core library

I posted a discussion in llama.cpp on this topic - hopefully we gather some insight on how to make such CI in the cloud:

https://github.com/ggerganov/llama.cpp/discussions/1985

Extra related issues:

• https://github.com/ggerganov/llama.cpp/issues/2631
• https://github.com/ggerganov/llama.cpp/issues/2634

TODOs:

• Add Metal CI to llama.cpp using the new macos-13 runners: https://github.com/ggerganov/ggml/pull/514