Removed const references for simple types and structures less 16 bytes

[GermanAizek]

As a minor improvement, std::string is made as param by constant reference, and probs_iterator tmp has become constant iterator.

In general, passing simple types and objects less than 16 bytes by reference makes optimization worse by modern compiler because it strictly follows rules programmer. I don't know if this will affect -O2 and even more so -O3.

Reference: https://stackoverflow.com/a/3314034

[GermanAizek]

@JohannesGaessler, I'm sorry, I accidentally called you to do a code review.

[ggerganov]

Keep only the changes in common/arg.cpp and ggml/src/gguf.cpp. The others are either not improvements or would just create conflicts with more important changes.