strip fancy api for now

the api has an unsound problem. The `Parser` trait is implemented on the
`&Operator` but inside `parse_next` a mutable ref and
`ReffCell::borrow_mut` are used which can lead to potential problems.

We can return to the API later. But for now lets keep only the essential
algorithm and pass affix parsers as 3 separate entities

Also add left_binding_power and right_binding_power to the operators
based on
winnow-rs#614 (comment)