## Summary
Now that `get_or_build_wheel` will often _also_ handle the unzip step,
we need to move our per-target locking (`OnceMap`) up a level.
Previously, it was only applied to the unzip step, to prevent us from
attempting to unzip into the same target concurrently; now, it's applied
at the `get_wheel` level, which includes both downloading and unzipping.
## Test Plan
It seems like none of our existing tests catch this -- perhaps because
they're too "simple"? You need to run into a situation in which you're
doing multiple source distribution builds concurrently (since they'll
all try to download `setuptools`):
```
rm -rf foo && virtualenv --clear .venv && cargo run -p puffin-cli -- pip-compile ./scripts/requirements/pydantic.in --verbose --cache-dir foo
```
Charlie Marsh
35c1faa575