Add atom var

[logseq-cldwalker]

Hi @borkdude. The motivation for adding this to nbb is I'd like to be able to check if something is an Atom e.g. (instance? cljs.core/Atom state). While loading this file into nbb, this was the only cljs code that couldn't load normally. I didn't add a test since I didn't see any for just var additions but happy to do so if you'd like

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Please answer the following questions and leave the below in as part of your PR.

• [x] I have read the developer documentation.

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• [ ] This PR contains a test to prevent against future regressions

• [x] I have updated the CHANGELOG.md file with a description of the addressed issue.

[borkdude]

Can you add a test as well? It's not obvious that the instance check will succeed.

[logseq-cldwalker]

Sure. Added

[borkdude]

Thanks! I assume you don't need a new release since you build your own nbb-logseq right?

[logseq-cldwalker]

Yep! There's no rush for a new release