Gazelle: PEP 723 Support?

# 🚀 feature request

### Relevant Rules

`gazelle`

### Description

With [PEP 723](https://peps.python.org/pep-0723/) approved, should we do something with that with gazelle?

### Describe the solution you'd like

Thoughts:

+ Maybe we read all files and add any PEP 723 deps to an "effective" requirements lock file?
+ Parse the PEP 723 deps and add to the `deps` attribute? How is this different from parsing `import`?
+ might be an alternative to the annotation `# gazelle:include_dep @pypi//foo` within a python file.
+ ???

### Describe alternatives you've considered

None.

Start by reviewing Gazelle's current Python dependency handling, including import parsing, the deps attribute, and # gazelle:include_dep annotations, then compare that with PEP 723 dependency metadata. Done requires an agreed scope and behavior for PEP 723 support, backed by tests; the issue names no files or test entry points.

索引モデルが issue の本文から書いたものです。