Feature/user choice sample tensor

[michele-milesi]

Summary

Describe the purpose of the pull request, including:

• Added the buffer.from_numpy parameter to let the user decide which function to use to convert Numpy arrays into PyTorch tensors when the to_tensor() and sample_tensors() functions are called.
  In particular, it is used the torch.from_numpy() function when buffer.from_numpy=True, otherwise the torch.as_tensor() function.

Type of Change

Please select the one relevant option below:

• New feature (non-breaking change that adds functionality)

Checklist

Please confirm that the following tasks have been completed:

• I have tested my changes locally and they work as expected. (Please describe the tests you performed.)
• I have added unit tests for my changes, or updated existing tests if necessary.
• I have updated the documentation, if applicable.
• I have installed pre-commit and run locally for my code changes.