ffcv installation issues

[ricvolpi]

Hey, thanks for releasing the code.

I've some issues installing ffcv in the env created following your instructions. All the rest works properly.

Collecting ffcv==0.0.3
  Using cached ffcv-0.0.3.tar.gz (53 kB)
  Preparing metadata (setup.py) ... error
  error: subprocess-exited-with-error
  
  × python setup.py egg_info did not run successfully.
  │ exit code: 1
  ╰─> [8 lines of output]
      Traceback (most recent call last):
        File "<string>", line 2, in <module>
        File "<pip-setuptools-caller>", line 34, in <module>
        File "/tmp/pip-install-4acbaiqr/ffcv_881eb017aa794ce48382a101ccbbb4f6/setup.py", line 30, in <module>
          extension_kwargs = pkgconfig('opencv4', extension_kwargs)
        File "/tmp/pip-install-4acbaiqr/ffcv_881eb017aa794ce48382a101ccbbb4f6/setup.py", line 18, in pkgconfig
          raise Exception()
      Exception
      [end of output]
  
  note: This error originates from a subprocess, and is likely not a problem with pip.
error: metadata-generation-failed

× Encountered error while generating package metadata.
╰─> See above for output.

note: This is an issue with the package mentioned above, not pip.
hint: See above for details.

Seems something related to opencv, that though is properly installed. Did this ever happen to you? Thanks.