enable string_slice lint

Also swaps out vendored HTML-escaping code for a dependency that I
imagine has decent testing considering all of its reverse depedencies.

src/api/client_server/report.rs

@@ -1,4 +1,4 @@
-use crate::{services, utils::HtmlEscape, Error, Result, Ruma};
+use crate::{services, Error, Result, Ruma};
 use ruma::{
     api::client::{error::ErrorKind, room::report_content},
     events::room::message,
@@ -61,7 +61,7 @@ pub(crate) async fn report_event_route(
                 pdu.room_id,
                 pdu.sender,
                 body.score,
-                HtmlEscape(body.reason.as_deref().unwrap_or(""))
+                html_escape::encode_safe(body.reason.as_deref().unwrap_or(""))
             ),
         ));
 

src/api/server_server.rs

@@ -107,7 +107,7 @@ impl FedDest {
     fn port(&self) -> Option<u16> {
         match &self {
             Self::Literal(addr) => Some(addr.port()),
-            Self::Named(_, port) => port[1..].parse().ok(),
+            Self::Named(_, port) => port.strip_prefix(':').and_then(|x| x.parse().ok()),
         }
     }
 }