Add display of interpreter request (#3751)
e.g.
```
❯ echo "anyio" | cargo run -q -- pip compile - --python 3.9 -v
DEBUG Searching for interpreter that fulfills Python @ 3.9
DEBUG Found a virtual environment at: /Users/zb/workspace/uv/.venv
DEBUG Using Python 3.9.18 interpreter at bin/cpython-3.9.18-macos-aarch64-none/install/bin/python3 for builds
```
