implement defered loglet commit resolver (#1968)

crates/bifrost/src/loglet/mod.rs

@@ -154,6 +154,22 @@ pub trait LogletReadStream: Stream<Item = Result<LogEntry<LogletOffset>, Operati
 
 pub type SendableLogletReadStream = Pin<Box<dyn LogletReadStream + Send>>;
 
+#[allow(dead_code)]
+pub(crate) struct LogletCommitResolver {
+    tx: oneshot::Sender<Result<LogletOffset, AppendError>>,
+}
+
+#[allow(dead_code)]
+impl LogletCommitResolver {
+    pub fn sealed(self) {
+        let _ = self.tx.send(Err(AppendError::Sealed));
+    }
+
+    pub fn offset(self, offset: LogletOffset) {
+        let _ = self.tx.send(Ok(offset));
+    }
+}
+
 pub struct LogletCommit {
     rx: oneshot::Receiver<Result<LogletOffset, AppendError>>,
 }
@@ -170,6 +186,12 @@ impl LogletCommit {
         let _ = tx.send(Ok(offset));
         Self { rx }
     }
+
+    #[allow(dead_code)]
+    pub(crate) fn deferred() -> (Self, LogletCommitResolver) {
+        let (tx, rx) = oneshot::channel();
+        (Self { rx }, LogletCommitResolver { tx })
+    }
 }
 
 impl std::future::Future for LogletCommit {