fix: bake promtool into ci-full image, add download timeout, speed up tests

- Add promtool to ci-full Dockerfile so it's pre-installed in the
  runner image instead of downloaded at runtime on every infra CI run
- Add 60s timeout to _download() in install_tools.py to prevent
  indefinite hangs when GitHub release downloads stall
- Use -n 8 workers for test-unit target (3s vs 4s with auto/16)
- Update test_download to mock urlopen instead of urlretrieve

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

tests/unit/test_install_tools.py

@@ -47,13 +47,25 @@ class TestDownload:
     def test_download(self, tmp_path: Path) -> None:
         dest = tmp_path / "file.bin"
 
-        def _write_file(url: str, path: Path) -> tuple[str, None]:
-            Path(path).write_bytes(b"data")
-            return str(path), None
+        class _FakeResponse:
+            def __init__(self) -> None:
+                self._sent = False
 
-        with patch("urllib.request.urlretrieve", side_effect=_write_file) as mock_retrieve:
+            def __enter__(self) -> _FakeResponse:
+                return self
+
+            def __exit__(self, *args: object) -> None:
+                pass
+
+            def read(self, n: int = -1) -> bytes:
+                if self._sent:
+                    return b""
+                self._sent = True
+                return b"data"
+
+        with patch("urllib.request.urlopen", return_value=_FakeResponse()) as mock_urlopen:
             install_tools._download("https://example.com/file", dest)
-        mock_retrieve.assert_called_once()
+        mock_urlopen.assert_called_once()
         assert dest.read_bytes() == b"data"