Print dependencies in uv pip list.

[tjni]

Summary

This is controlled by the --requires and --required-by flags and only works when the output format is JSON.

This addresses part of #4711, but I agree with #4711 (comment) that it belongs in uv pip list instead of uv pip tree. A few notes about this:

1. I picked --requires and --required-by to match the Requires and Required-By fields that appear in the output of uv pip show.
2. I decided to return the dependencies as objects with a single field called name. This leaves the door open to add more fields to each dependency in the future, such as installed version and requested versions.

I'm hoping to get some early feedback on this PR to test the temperature of this approach, before I proceed. The remaining work as I see it currently includes:

• Add tests for this feature.
• Add documentation for this feature.
• Better error messages (e.g. if used with the default column format, perhaps suggest uv pip tree instead).
• Any code review suggestions (I'm a Rust novice).

Test Plan

[tjni]

As I was doing more research about this, I noticed that pypa/pip#11097 is prior art, where incorporating arbitrary metadata into the output of pip list was rejected in favor eventually of pip inspect. This brings up the question to us too about where to draw the line about what to include under this command. I'm not sure.