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This PR adds some additional reasons for deprecate/disable in casks.

I would expect that discontinued would be used when a software is officially discontinued upstream, unmaintained used when a software has not received updates for a long time and may not work as expected on modern hardware, and no_longer_available when the software can longer be sourced from upstream.

It could be worth considering a no_longer_works style option, however this likely overlaps with unmaintained.