Add CatSystem2 `.zt` extension archive format (*CatSystem2 pack file*).
* Usage: Extras/export pack files for CatSystem2 - often used to save wallpapers, wav files, or other extras to the user's computer.
* Tag: `ZT/PACK` (chosen over *just* `ZT`, based on the devkit tool name: `ztpack.exe`, which also describes it as a *"pack file"*).
* Extension: `*.zt` (found in `export.int` archive).
* Signature: No file signature of any kind, immediately starts with an entry structure. A lot of sanity checks have been added.
* Hierarchic: Yes, although this is rarely used, and CS2's implementation is rather buggy.
* Buggy enough that Frontwing gave up and started putting zip files **into** zt files!
* The specification at least, is still well defined.
* Archive layout is the standard offset-next approach seen in other CS2 formats. But there's two offset-next fields, one for subdirectory entries, and one for the next flat (current) directory entry.
* Folders have their own entries, which are what point to child file entries.
