PowerPC seems to build without errors if we upgrade `zlib-ng`, but
upgrading `zlib-ng` causes Windows to break
(https://github.com/rust-lang/libz-sys/issues/225), and Cargo doesn't
let us include two different versions.
s390x fails because it can't find `stfle`. It's possible that we could
fix this by by upgrading our manylinux version and/or by upgrading GCC
(which may necessitate upgrading our manylinux version), but I don't
know if it's fixable without one of those things? And it's not worth
bumping compatibility for that reason. \cc @konstin
As per
https://matklad.github.io/2021/02/27/delete-cargo-integration-tests.html
Before that, there were 91 separate integration tests binary.
(As discussed on Discord — I've done the `uv` crate, there's still a few
more commits coming before this is mergeable, and I want to see how it
performs in CI and locally).
