Function generate_atom_feed 

fn generate_atom_feed(
    project_name: &str,
    versions: &[VersionInfo],
    base_url: Option<&str>,
    changelog_sections: &HashMap<String, String>,
) -> String

Generate an Atom 1.0 feed listing all known releases.

• base_url: when provided (already stripped of trailing /), used to build <link> and <id> elements with absolute URLs. When absent, a urn: based ID is used and no <link> elements are emitted.
• changelog_sections: map from version string to Markdown release-note body. When a matching entry is found it is rendered to HTML and included as a <content type="html"> element in the Atom entry.