shichizip-zs 0.2.0 (new cask)

[szw0407]

Add ShichiZipZS, a new Cask. I have tested it with Homebrew 5.1.11-96-g0410293.

Additional notes:

• ShichiZipZS is the Zstandard fork variant of ShichiZip, officially built and released by upstream alongside the mainline build on every release. It is not a third-party repackage — both ship from the same repo (idawnlight/ShichiZip).
• The two variants are functionally distinct: the ZS build is compiled adding Zstandard compression support absent in mainline. Users working with .zst archives may require this specific binary.
• This cask is prepared with reference to the merged shichizip cask, shichizip 0.1.6 (new cask) #263599. This PR is advised as discussed in idawnlight/ShichiZip#22.
• It's my first attempt to commit to this project, and I am willing to help fix any issues if exist. Thanks.

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• AI was used to generate or assist with generating this PR. Please specify below how you used AI to help you, and what steps you have taken to manually verify the changes, including zap stanza paths.

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