Add a mask-setter property

[keflavich]

This error: https://github.com/radio-astro-tools/spectral-cube/actions/runs/4375133747/jobs/7655452694#step:5:2644 may be caused by not having a settable mask.

We really need to resolve this with the https://github.com/radio-astro-tools/spectral-cube/pull/808 refactor, but I want passing tests as a stopgap

[codecov-commenter]

Codecov Report

Patch coverage: 66.66% and project coverage change: -0.01 :warning:

Comparison is base (d004d79) 77.36% compared to head (66ccaa9) 77.36%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #869 +/- ## ========================================== - Coverage 77.36% 77.36% -0.01% ========================================== Files 24 24 Lines 6027 6030 +3 ========================================== + Hits 4663 4665 +2 - Misses 1364 1365 +1 ``` | [Impacted Files](https://codecov.io/gh/radio-astro-tools/spectral-cube/pull/869?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=radio-astro-tools) | Coverage Δ | | |---|---|---| | [spectral\_cube/base\_class.py](https://codecov.io/gh/radio-astro-tools/spectral-cube/pull/869?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=radio-astro-tools#diff-c3BlY3RyYWxfY3ViZS9iYXNlX2NsYXNzLnB5) | `85.93% <66.66%> (-0.18%)` | :arrow_down: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=radio-astro-tools). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=radio-astro-tools)

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[keflavich]

I'm going to merge this into #854 and try to resolve everything there

[e-koch]

@keflavich good to close this in favour of #854?

[keflavich]

Yep.