Improve CLI documentation for uv run

[zanieb]

Adds more long-form help to uv run, which renders in uv help run and the CLI reference on the website.

[charliermarsh]

I don't think this applies to inline metadata, does it?

[zanieb]

I'm not sure. You can have a tool.uv section? I guess I'll check

[charliermarsh]

I don't think we would respect that, because we return:

/// PEP 723 metadata as parsed from a `script` comment block.
///
/// See: <https://peps.python.org/pep-0723/>
#[derive(Debug, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case")]
pub struct Pep723Metadata {
    pub dependencies: Vec<pep508_rs::Requirement<VerbatimParsedUrl>>,
    pub requires_python: Option<pep440_rs::VersionSpecifiers>,
}

[zanieb]

Yeah I confirmed we do not, which is debatably wrong. I'm fine with not reading [tool.uv.dev-dependencies] but we do need to respect [tool.uv] settings: #5855