Add a progress bar for rsync

On a terminal, run rsync with --info=progress2 and draw its updates as a
progress bar on stderr. The ETA is estimated locally, since rsync reports
the elapsed time when a file finishes. Disable it with --no-progress.

tests/test_cli.py

@@ -27,7 +27,7 @@ class FakeBackup:
     def __init__(self, inputs: Any, output: Any, exclude: Any, keep: Any, options: str,
                  ssh_host: Optional[str] = None, ssh_user: Optional[str] = None,
                  ssh_keyfile: Optional[str] = None, remote_sudo: bool = False,
-                 remove_before: bool = False, verbose: bool = False) -> None:
+                 remove_before: bool = False, verbose: bool = False, progress: bool = False) -> None:
         self.inputs = inputs
         self.output = output
         self.exclude = exclude
@@ -39,6 +39,7 @@ class FakeBackup:
         self.remote_sudo = remote_sudo
         self.remove_before = remove_before
         self.verbose = verbose
+        self.progress = progress
         self.homedir: Optional[str] = None
         self.ran = False
         self.closed = False
@@ -224,6 +225,18 @@ ssh_keyfile=/keys/id
         b = last_backup()
         assert b.remote_sudo and b.remove_before and b.verbose
 
+    @pytest.mark.parametrize('tty, argv, progress', [
+        (True, [], True),
+        (True, ['--no-progress'], False),
+        (False, [], False),
+    ])
+    def test_progress(self, run_cli: RunCli, config: Callable[[str], str], monkeypatch: pytest.MonkeyPatch,
+                      tty: bool, argv: list[str], progress: bool) -> None:
+        monkeypatch.setattr(sb.sys.stderr, 'isatty', lambda: tty)
+
+        assert run_cli('-c', config('backup_dir=/backups'), *argv) == 0
+        assert last_backup().progress is progress
+
     def test_check_params_failure(self, run_cli: RunCli, config: Callable[[str], str]) -> None:
         FakeBackup.check_code = 2