Radboud: per-file completion log so small files are visible

Previously the prefetch_files banner said "Downloading 12 files" but
only files >= 10 MB got a per-byte progress bar (everything else
downloaded silently to avoid bar spam). The result looked like only
one file was actually transferring even though all 12 were.

Now every completed download prints a one-line entry:

  Radboud WebDAV: downloading 12 file(s)…
    [1/12] BadChannels (0 B)
    [2/12] sub-A2002_task-rest_meg.meg4 (530 MB)
    ...
  Radboud WebDAV: done (12/12 files).

The per-byte tqdm bar still shows for files >= 10 MB (the .meg4 chunk
is what the user actually wants to watch).

Author: Gereon Elvers

pnpl/datasets/mixins/radboud_download.py

@@ -159,17 +159,44 @@ def _join_url(cls, rel_path: str) -> str:
 
     def prefetch_files(self, file_paths: list[str]) -> None:
         """Prefetch multiple files in parallel (skips already-present)."""
-        futures = []
-        for fpath in {p for p in file_paths if not os.path.exists(p)}:
-            futures.append(self._schedule_download(fpath))
-        if futures:
-            print(f"Downloading {len(futures)} files from Radboud WebDAV...")
-            for future in futures:
-                try:
-                    future.result()
-                except Exception as e:
-                    print(f"Error downloading a file: {e}")
-            print("Done!")
+        # De-dupe + drop already-present files, but keep a stable order
+        # so the per-file completion log reads naturally.
+        seen: set[str] = set()
+        targets: list[str] = []
+        for fpath in file_paths:
+            if fpath in seen or os.path.exists(fpath):
+                continue
+            seen.add(fpath)
+            targets.append(fpath)
+        if not targets:
+            return
+
+        n = len(targets)
+        type(self)._log(f"Radboud WebDAV: downloading {n} file(s)…")
+
+        # Schedule the whole batch up front so the executor starts
+        # parallel downloads before we begin waiting on results.
+        scheduled = [(fpath, self._schedule_download(fpath)) for fpath in targets]
+
+        completed = 0
+        for fpath, future in scheduled:
+            try:
+                future.result()
+                completed += 1
+                # Always emit a per-file completion line — small files
+                # don't get a per-byte progress bar (we suppress it for
+                # anything < 10 MB to avoid bar spam) but users still
+                # need to see the batch advancing.
+                size = os.path.getsize(fpath) if os.path.exists(fpath) else None
+                size_str = type(self)._format_bytes(size)
+                type(self)._log(
+                    f"  [{completed}/{n}] {os.path.basename(fpath)} ({size_str})"
+                )
+            except Exception as exc:
+                type(self)._log(
+                    f"  [error] {os.path.basename(fpath)}: {exc}"
+                )
+        type(self)._log(f"Radboud WebDAV: done ({completed}/{n} files).")
 
     def ensure_file(self, fpath: str) -> str:
         """Ensure a file exists locally, downloading via WebDAV if needed."""