Fix hashes should be hex not base64

[danyeaw]

Description

Closes #249.

Wheel RECORD includes the hash value as a base64 encoded value per PEP 376 and updated in the Python Package User Guide which includes hash algorithm followed by the equals character =, followed by the urlsafe-base64-nopad encoding of the digest with trailing = removed.

When unpacking an archive, conda creates metadata for each package in its conda-meta/<package.json> file in the paths_data section. The format of this hash is a hex value (the standard sha256sum format) of the sha256 for the sha256 and sha256_in_prefix fields.

The wheel package extractor was taking the hashes from the wheels RECORD and putting it in to the conda metadata directly while unpacking the .whl. This resulted in base64 hashes to appear in conda metadata and resulted in a ValueError when conda-rattler-solver tried to transform the hashes from a conda prefix record to a rattler prefix record.

Since we were also computing hashes in the build module, I centralized the hash calculations in to the utils module and added unit tests for them.

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[codspeed-hq]

Merging this PR will not alter performance

✅ 5 untouched benchmarks

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_{Comparing fix-conda-hash (494f85b) with main (43b0aea)}

[ForgottenProgramme]

Thanks for creating this, @danyeaw.
I looked through the PR and I find some of the tests redundant. Added comments pointing those out.

[ForgottenProgramme]

LGTM!
Suggestions made by other reviewers are all relevant and can be tracked in different tickets. 👍🏼