The Valve Binary Space Partition file format in Kaitai Struct.

<details><summary><h2>Context</h2></summary> <a href="https://kaitai.io/#what-is-it">Kaitai Struct</a> is a language used to describe binary file formats.</details>

I still need to add the lump types; but I haven't because I've been so busy (and also executive dysfunction is messing with me).