feat: Improve performance of built-in-functions via static regexes - #249

Description

Instantiation of std::regex involves parsing and compiling the regular expression and should therefore be considered "expensive".

In this PR I changed some constant std::regex in the built-in-functions to static variables and moved those that are used multiple times to an anonymous namespace. I also introduced a few functions to reduce code duplication.

In the specific use case, this was tested with 1000 different requests. These were structured in such a way that the entire policy had to be run through each time.
The time saving was around 40%.
casbintest runs about 25% faster.

I tried to reflect functionality of the regex-expressions in the variable-names.

Testimonials

Unmodified version:

$ time ./casbintest >/dev/null

real    0m2.333s
user    0m1.968s
sys     0m0.230s

With this change:

$ time ./casbintest >/dev/null

real    0m1.733s
user    0m1.260s
sys     0m0.180s