Fix BatchProcessor ordering in MultiBatchProcessor

[SirYwell]

Overview

Description

I noticed that the order is based on HashMap, which does not make any guarantees about value iteration order. EnumMap is a better choice as it guarantees iteration order in the natural order of the enum values.

### Submitter Checklist
- [x] Make sure you are opening from a topic branch (**/feature/fix/docs/ branch** (right side)) and not your main branch.
- [x] Ensure that the pull request title represents the desired changelog entry.
- [x] New public fields and methods are annotated with `@since TODO`.
- [x] I read and followed the [contribution guidelines](https://github.com/IntellectualSites/.github/blob/main/CONTRIBUTING.md).