refactor: remove test redundancy, reduce API surface

- Remove duplicate xml_escape tests from sitemap.rs and feed.rs
  (already tested in escape.rs)
- Make html_escape_into private (only used internally)

src/escape.rs

@@ -12,7 +12,7 @@ pub fn html_escape(s: &str) -> String {
 /// Escape HTML characters into an existing string.
 ///
 /// This is more efficient when building output incrementally.
-pub fn html_escape_into(out: &mut String, s: &str) {
+fn html_escape_into(out: &mut String, s: &str) {
     for c in s.chars() {
         match c {
             '&' => out.push_str("&"),

src/feed.rs

@@ -80,14 +80,3 @@ pub fn generate_atom_feed(
         entries,
     )
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_xml_escape() {
-        assert_eq!(xml_escape("Hello & World"), "Hello & World");
-        assert_eq!(xml_escape("<tag>"), "&lt;tag&gt;");
-    }
-}

src/sitemap.rs

@@ -93,14 +93,6 @@ fn build_sitemap_xml(entries: &[SitemapEntry]) -> String {
 mod tests {
     use super::*;
 
-    #[test]
-    fn test_xml_escape() {
-        assert_eq!(xml_escape("Hello & World"), "Hello & World");
-        assert_eq!(xml_escape("<tag>"), "&lt;tag&gt;");
-        assert_eq!(xml_escape("\"quoted\""), "&quot;quoted&quot;");
-        assert_eq!(xml_escape("it's"), "it&apos;s");
-    }
-
     #[test]
     fn test_build_sitemap_xml_single_entry() {
         let entries = vec![SitemapEntry {