Show time taken instead of eta 0:00:00 after download completion (#13486)

This is more useful than seeing eta 0:00:00.

There is an extra space left over, but there isn't much we can do about
that unfortunately. It'd be nice if Rich wouldn't add the space if the
column was empty, but looking at their codebase, such a change seems
nontrivial.

Co-authored-by: asai-r <[email protected]>

Author: qraqras

news/13483.feature.rst

@@ -0,0 +1 @@
+Show time taken instead of ``eta 0:00:00`` at download completion.

src/pip/_internal/cli/progress_bars.py

@@ -53,18 +53,21 @@ def _rich_download_progress_bar(
             BarColumn(),
             DownloadColumn(),
             TransferSpeedColumn(),
-            TextColumn("eta"),
-            TimeRemainingColumn(),
+            TextColumn("{task.fields[time_description]}"),
+            TimeRemainingColumn(elapsed_when_finished=True),
         )
 
     progress = Progress(*columns, refresh_per_second=5)
-    task_id = progress.add_task(" " * (get_indentation() + 2), total=total)
+    task_id = progress.add_task(
+        " " * (get_indentation() + 2), total=total, time_description="eta"
+    )
     if initial_progress is not None:
         progress.update(task_id, advance=initial_progress)
     with progress:
         for chunk in iterable:
             yield chunk
             progress.update(task_id, advance=len(chunk))
+        progress.update(task_id, time_description="")
 
 
 def _rich_install_progress_bar(