Security of wheel variants

tl;dr: Variant providers will run no untrusted code by default. There will be a shared list of heavily vetted providers for tools to vendor or reimplement. For everything beyond that, user opt-in is required. The security story of wheel variants was heavily discussed as part of the previous PEP 817 thread. Here we want to propose an updated design that balances security and user experience. To recap, we want to introduce advanced platform support, especially GPU support. Instead of hardcoding ...