Bypass cp alias in visualize_tests approve command

Many shells alias cp to cp -i, which prompts before overwriting an
existing baseline image — annoying when approving multiple failing
tests in one paste. Prefix the generated cp lines with a backslash so
the shell skips the alias and runs the binary directly.

Author: has2k1

tools/visualize_tests.py

@@ -577,7 +577,7 @@ def get_test_images() -> Iterator[TestImage]:
       const file = r.dataset.file;
       subdirs.add(sub);
       lines.push(
-        'cp tests/result_images/' + sub + '/' + file +
+        '\\\\cp tests/result_images/' + sub + '/' + file +
         ' tests/baseline_images/' + sub + '/' + file
       );
     }