By default it will create hard links for python packages, so it won't consume any more memory (besides the small overhead of hard links).
I plan on offering this kind of cached precompiled bytecode in PAPER, but I know that compiled bytecode includes absolute paths (used for displaying stack traces) that will presumably then refer to the cached copies. I'll want to test as best I can that this doesn't break anything more subtle.
Ironically, if my backup scheme were using hard links, then I could simply exclude the cache directory from backup, so I’d have no reason to do that mountpoint spiel, and uv’s hard links would work normally.
You’re correct, ZFS snapshots don’t produce copies, at least not at the time they’re being created. They work a little like copy-on-write.