common : move arg parser code to `arg.cpp` (#9388)

* common : move arg parser to arg.cpp

* better categorize args

* add cmake

* missing climits

* missing cstdarg

* common : more explicit includes

* fix build

* refactor gpt_params_parse

* update server readme

* fix test

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Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>