refactor(cache): further condense walkTree

[agilgur5]

Summary

Condense walkTree further to just 4 LoC

• Follow-up to refactor(cache): tiny simplification to walkTree #359 I guess

Details

• forEach returns void, so we can just return it and condense the if a bit

[ezolenko]

Feels weird to return void, but I guess TS will warn if return types ever get out of sync 🤷

[agilgur5]

Yea it's a stylistic thing; I thought it seemed odd in the context of this codebase but I've written code like this in other codebases where it doesn't seem as "out of place".
Changing some of the style in this and #402 should make it feel more comfortable.

Should probably get prettier (or another formatter) into this codebase at some point to make everything more consistent (and switch to non-deprecated ESLint too 😅)