CIF Parser

The cif module is a standalone CIF/STAR parser with typed data extraction. It operates in two layers.

Layer 1 — DOM parsing (`cif::parse`)

let doc = molex::cif::parse(input)?;

Parses any CIF or STAR file into an untyped Document tree:

Document contains Vec<Block>
Each Block has name, categories (loop tables), and pairs (key-value entries)
Category holds Column data (string values, one per row)

This layer makes no assumptions about the content — it works for mmCIF, CCD, reflection data, or any STAR-format file.

Layer 2 — Typed extractors (`cif::extract`)

Pull structured data from a parsed Block:

use molex::cif::extract::{CoordinateData, CifContent};

// Caller knows the content type:
let coords = CoordinateData::try_from(&block)?;

// Or auto-detect:
match CifContent::try_from(&block)? {
    CifContent::Coordinates(data) => { /* atom_site data */ },
    CifContent::Reflections(data) => { /* refln data */ },
    CifContent::Dictionary(data)  => { /* CCD entry */ },
}