Investigate generics usage in parser and engine packages

[jalseth]

Conftest does a lot of similar operations for the various config languages it supports. It may be possible to implement some of this using generics rather than having the same logic implemented over and over.

cc @boranx

[jalseth]

A function signature for the parser may look something like func parse[T any](data []byte, unmarshal func([]byte, T) error) (map[string]any, error) { ... }

[boranx]

yeah, +1 to be using the new form among the parsers.
One caveat is that conftest consumers would need to refactor their code to apply the new form if they depend on parser, still, I think we can mention it in the release notes to spread the change gracefully