[REFACTORING] Operator Grammar / Implementation

[rhazn]

• refactor this grammar to be more clearly readable (e.g. move all binary / ternary expressions into one type, have an easy and clear way to define order of execution instead of this weird setup of referring to the next lower expression)
• add tests
• refactor implementation to be less verbose / easier to read / less copy and paste between binary and ternary operators

See discussion in https://github.com/jvalue/jayvee/pull/521