Fix cargo clippy and doc errors after Rust update to 1.66

src/html.rs

@@ -234,7 +234,7 @@ impl HtmlMsgParser {
 /// Convert a mime part to a data: url as defined in [RFC 2397](https://tools.ietf.org/html/rfc2397).
 fn mimepart_to_data_url(mail: &mailparse::ParsedMail<'_>) -> Result<String> {
     let data = mail.get_body_raw()?;
-    let data = base64::encode(&data);
+    let data = base64::encode(data);
     Ok(format!("data:{};base64,{}", mail.ctype.mimetype, data))
 }