## Summary
Closes#1977
This allows us to send uv's version in the `uv-client` User Agent
header.
Here's how request headers look like to a server now:
```
...
Accept: application/vnd.pypi.simple.v1+json, application/vnd.pypi.simple.v1+html;q=0.2, text/html;q=0.01
User-Agent: uv/0.1.13
...
```
~~I went for a mix of Option 1 and 2 from #1977.~~ Open to alternative
naming as well, not tied too strongly here to the names picked.
~~Another possibility for this new crate is that we can use it to
consolidate metadata that exists across crates to ultimately be able to
create linehaul information described in #1958, but I haven't looked
into what those changes might look like.~~
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## Test Plan
<!-- How was it tested? -->
Added initial tests in the new crate to exercise its public API and
added a new test to uv-client to validate the headers using a 1-time
disposable server.
