Respect HTTP client options when reading remote requirements files (#2434)
Uses the base client introduced in #2431 to restore use of our fully
configured client when reading remote requirements files.
Closes https://github.com/astral-sh/uv/issues/2357
## Test plan
```
npx http-server --username user --password password
cargo run -- pip install -r http://user:password@127.0.0.1:8080/requirements.txt
```
Fails on main succeeds on branch.