feat: tracel-artifact uploads parts concurrently

crates/tracel-artifact/src/transfer/mod.rs

@@ -38,8 +38,9 @@ mod ranged;
 /// Watches a transfer as it runs, and can stop it.
 ///
 /// Every method defaults to doing nothing, so an implementation only has to define the events it
-/// cares about. Callbacks run on the transferring thread and block it, so an implementation that
-/// does real work should hand it off.
+/// cares about. Callbacks run on the thread that started the transfer and block it, so an
+/// implementation that does real work should hand it off. An upload sends several parts at once,
+/// so it can report on more than one file at a time; each call names its file.
 pub trait TransferObserver {
     /// Returns whether the active transfer should stop.
     ///
@@ -55,8 +56,8 @@ pub trait TransferObserver {
         let _ = (rel_path, total_bytes);
     }
 
-    /// Bytes have moved for the file being transferred. `transferred_bytes` is the running total
-    /// for that file, not an increment.
+    /// Bytes have moved for the file `rel_path`. `transferred_bytes` is the running total for that
+    /// file, not an increment.
     fn file_progress(&mut self, rel_path: &str, transferred_bytes: u64) {
         let _ = (rel_path, transferred_bytes);
     }