Restructure `parser.hpp`

[ThoSe1990]

parser.hpp is entirely static free functions in a header. This is a ~350-line header that's essentially an implementation file. It works, but it means recompilation of anything that includes it when any parsing logic changes, and it's a bit unusual.

[geekaman243]

I want to work on this issue.
Please assign this issue to me.

[ThoSe1990]

Sorry for the late reply, and thanks for your interest :)

I assigned it to you, it shouldn't be a lot of work. Making all the static functions where the parser is passed by reference to private member function should be enough.

[geekaman243]

I will start working