Add PEP 723 support to uv run

[charliermarsh]

Closes #3096

Summary

Enables uv run foo.py to execute PEP 723-compatible scripts.

For example, given:

# /// script
# requires-python = ">=3.11"
# dependencies = [
#   "requests<3",
#   "rich",
# ]
# ///

import requests
from rich.pretty import pprint

resp = requests.get("https://peps.python.org/api/peps.json")
data = resp.json()
pprint([(k, v["title"]) for k, v in data.items()][:10])

[charliermarsh]

There are some refactors I want to do as a follow-up.

[charliermarsh]

Should we suppress output here...?

[charliermarsh]

I will DRY this up separately, I need to audit the usages.