Dataset downloading expected behavior pt. 2

When I instantiate a dataset with download=False and checksum=False I expect it to assume everything is in place, however our current setup usually checks to make sure that the archive file exists. If the archive file is 100+ GB then it is totally reasonable for users to delete it but keep the downloaded data.

I think _check_integrity should be something like this:

    def _check_integrity(self) -> bool:
        """Check integrity of dataset.

        Returns:
            True if dataset MD5s match, else False
        """
        return check_integrity(
            os.path.join(self.root, self.filename),
            self.md5,
        )

and we only call it if self.checksum is true.

Datasets that still use _check_integrity (and presumably follow the old convention):

• Advance
• Benin Cashews
• CBF
• COWC
• CV4A Kenya
• Cyclone
• ETCI 2021
• Eurosat
• GID15
• LEVIRCD
• Loveda
• VHR10
• SEN12MS
• So2Sat
• SpaceNet
• UCMerced

For a good example to copy, I think CDL is the first dataset I updated to use the new download style.

[calebrob6]

I think we need a list here of all datasets that do not follow these conventions / a good example dataset to copy.

[calebrob6]

@estherrolf (one of our first users!) just hit this problem with a manually downloaded version of the ChesapeakeCVPR dataset. I think it is worth making the change as this will happen especially with the larger datasets.