federation-api: Move Visitor declaration into deserialize function

ruma-federation-api/src/serde/pdu_process_response.rs

@@ -7,6 +7,12 @@ use serde::{
     Deserialize, Serialize,
 };
 
+#[derive(Deserialize, Serialize)]
+struct WrappedError {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    error: Option<String>,
+}
+
 pub fn serialize<S>(
     response: &BTreeMap<EventId, Result<(), String>>,
     serializer: S,
@@ -33,18 +39,9 @@ pub fn deserialize<'de, D>(
 where
     D: Deserializer<'de>,
 {
-    deserializer.deserialize_map(PduProcessResponseVisitor)
+    struct PduProcessResponseVisitor;
-}
 
-#[derive(Deserialize, Serialize)]
+    impl<'de> Visitor<'de> for PduProcessResponseVisitor {
-struct WrappedError {
-    #[serde(skip_serializing_if = "Option::is_none")]
-    error: Option<String>,
-}
-
-struct PduProcessResponseVisitor;
-
-impl<'de> Visitor<'de> for PduProcessResponseVisitor {
         type Value = BTreeMap<EventId, Result<(), String>>;
 
         fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
@@ -66,6 +63,9 @@ impl<'de> Visitor<'de> for PduProcessResponseVisitor {
             }
             Ok(map)
         }
+    }
+
+    deserializer.deserialize_map(PduProcessResponseVisitor)
 }
 
 #[cfg(test)]