Modifications to merge logic

[zachdaniel]

Contributor checklist

• Bug fixes include regression tests
• Chores
• Documentation changes
• Features include unit/acceptance tests
• Refactoring
• Update dependencies

[zachdaniel]

@pinetops In an effort not to lose your work, this PR is made with your original commit retained :)

Now, we can modify ash and reactor to have merge_with: [Reactor.Error] and merge_with: [Ash.Error] respectively, and this should have the behavior you want.

I did add some flattening logic, but I think what I've added is a bit simpler overall, and only has to happen when an error class is produced.

[pinetops]

Wonderful. Thankyou!