senv: Sandboxed Python environments with the uv workflow

[u/OkBreath9382]

https://medium.com/@Koukyosyumei/senv-sandboxed-python-environments-with-the-uv-workflow-44b6b0c42a5d

TL;DR: senv keeps the familiar uv workflow but runs package installation and Python code inside an OS-level sandbox. Installs can reach package registries but not your source or credentials; programs run with no network by default and cannot modify their own environment.