Restrict observed requirements to direct when `--no-deps` is specified (#3191)
## Summary
This PR avoids: (1) using the lookahead resolver when `--no-deps` is
specified (we'll never use those requirements), and (2) including any
transitive requirements when searching for allowed URLs, etc., when
`--no-deps` is specified.
Closes https://github.com/astral-sh/uv/issues/3183.