Clean up batch actions code

[eemeli]

Minor cleanup, mostly focused on getting rid of the ACTIONS_FN_MAP that adds unnecessary indirection when handling batch actions.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 87.50000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.67%. Comparing base (7cc1d46) to head (f80fefe).
⚠️ Report is 1 commits behind head on main.

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[mathjazz]

What's the motivation for this change?

It will likely clash with #4152, which has been open for a while.

[eemeli]

Got annoyed at how much indirection I had to work through while figuring out if some of the changes I was applying required changes to the batch actions code.

I don't really have anything blocking on this, so would be happy to leave it open and see about resolving merge conflicts after #4152 is merged.