* fix: rename reproduce checksum file to SHA256SUMS.txt
Hugging Face renders relative links without a file extension as
directory links (/tree/), so the SHA256SUMS link in the reproduce
README opened a 404. Giving the file a .txt extension keeps the link
relative while making it open as a file, like the other reproduce
assets. The verification instruction becomes sha256sum -c SHA256SUMS.txt.
Fixes#463
* test: remove reproduce folder tests
