I saw warnings when we were e.g. unzipping wheel and setuptools in two
tasks at the same time. We now keep track of in flight unzips.
This introduces a `OnceMap` abstraction which we also use in the
resolver.
This is mostly a mechanical refactor that moves 80% of our code to the
same cache abstraction.
It introduces cache `Cache`, which abstracts away the path of the cache
and the temp dir drop and is passed throughout the codebase. To get a
specific cache bucket, you need to requests your `CacheBucket` from
`Cache`. `CacheBucket` is the centralizes the names of all cache
buckets, moving them away from the string constants spread throughout
the crates.
Specifically for working with the `CachedClient`, there is a
`CacheEntry`. I'm not sure yet if that is a strict improvement over
`cache_dir: PathBuf, cache_file: String`, i may have to rotate that
later.
The interpreter cache moved into `interpreter-v0`.
We can use the `CacheBucket` page to document the cache structure in
each bucket:

## Summary
This PR unifies the behavior that lived in the resolver's `distribution`
crates with the behaviors that were spread between the various structs
in the installer crate into a single `Fetcher` struct that is intended
to manage all interactions with distributions. Specifically, the
interface of this struct is such that it can access distribution
metadata, download distributions, return those downloads, etc., all with
a common cache.
Overall, this is mostly just DRYing up code that was repeated between
the two crates, and putting it behind a reasonable shared interface.
## Summary
This crate only contains types, and I want to introduce a new crate for
all _operations_ on distributions, so this feels like a more natural
name given we also have `pypi-types`.
This also allows us to get rid of `PinnedPackage` _and_ to remove some
`Result<...>` types due to needless conversions between
otherwise-identical types.
This is isn't ready, but it can resolve
`meine_stadt_transparent==0.2.14`.
The source distributions are currently being built serially one after
the other, i don't know if that is incidentally due to the resolution
order, because sdist building is blocking or because of something in the
resolver that could be improved.
It's a bit annoying that the thing that was supposed to do http requests
now suddenly also has to a whole download/unpack/resolve/install/build
routine, it messes up the type hierarchy. The much bigger problem though
is avoid recursive crate dependencies, it's the reason for the callback
and for splitting the builder into two crates (badly named atm)