core: improve calc evaluation

[sylvain101010]

What would you like to be changed

Why is this needed

Current evaluator is very, very, very, very basic

Libs

• https://github.com/rmoritz/calc-golang
• https://github.com/eamondunne/Calculator-Golang
• https://github.com/julz/calc
• https://github.com/alfredxing/calc
• https://github.com/antonmedv/expr
• https://github.com/PaesslerAG/gval
• https://github.com/Knetic/govaluate
• https://github.com/marcmak/calc
• https://github.com/maja42/goval