No module named 'visqol.pb2'

The installation using `bazel build :visqol -c opt` completed successfully without any errors.

After installation:

`from visqol import visqol_lib_py` works perfectly fine.

However when I tried `from visqol.pb2 import visqol_config_pb2`

or `from visqol.pb2 import similarity_result_pb2`

the error is
```
>>> from visqol.pb2 import visqol_config_pb2
Traceback (most recent call last):
File "", line 1, in
ModuleNotFoundError: No module named 'visqol.pb2'
```

Any ideas?