Use blocking reqwest API in defer

defer, or, trait functions such as it in general(?) cannot be async (yet)

plume-common/src/activity_pub/inbox.rs

@@ -279,7 +279,8 @@ pub trait FromId<C>: Sized {
 
     /// Dereferences an ID
     fn deref(id: &str) -> Result<Self::Object, (Option<serde_json::Value>, Self::Error)> {
-        reqwest::ClientBuilder::new()
+        // Use blocking reqwest API here, since defer cannot be async (yet)
+        reqwest::blocking::Client::builder()
             .connect_timeout(std::time::Duration::from_secs(5))
             .build()
             .map_err(|_| (None, InboxError::DerefError.into()))?