[FEATURE] AST for .nft files

It'd be useful, I think, to implement an AST for the `.nft` syntax files (e.g. [nftables scripts](https://wiki.nftables.org/wiki-nftables/index.php/Scripting)), and populating them as native types.

This would allow for rule evaluation and comparison against the current ruleset, identifying which file a rule is created in/included from, and even dumping representations to NFT snytax.

This would likely assist in tests and mocking as well.