How to handle major changes to directory structures

[Tremeschin]

I'm thinking of doing something similar to uv's buckets, where if a hard coded version number of their cache, archive, builds, interpreter etc, changes (see ~/.cache/uv/*-{v0,v1,v2,...}), it's safe to delete previous directories.

In pyaket's case, this is slightly harder to reason out, on any major dir changes no mix between old and newest versions of any project should be used together if we don't have the vN subdirectory. But also, it adds complexity needing to add a subcommand to delete old junk, and/or do it automatically (yet another .last_used tracker file similar to a version's venv). Ideally the user knows and manages that themselves, but we all know this ain't gonna happen.

I'm in favor of just having a single major structure file version and delete the whole thing if it mismatches, at the cost of breaking compatibility with mixed same projects versions, but the versioned artifacts isn't too hard to implement..