chore: implement PartialEq for most Snafu Error enums

[NickLarsenNZ]

Description

This change is to encourage testing error variants by type rather than text contents.

• Bump strum to 0.26.2
• Derive PartialEq on most Snafu Error enums.
• Add custom implementations of PartialEq for Snafu error enums that use types that are not directly comparable.

Important

Some variants are impossible to compare, so these implementations are restricted to #[cfg(test)] because they cause panics.

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

# Reviewer
- [ ] Code contains useful comments
- [ ] (Integration-)Test cases added
- [ ] Documentation added or updated
- [ ] Changelog updated
- [ ] Cargo.toml only contains references to git tags (not specific commits or branches)

# Acceptance
- [ ] Feature Tracker has been updated
- [ ] Proper release label has been added

[Techassi]

Looking good! Only requires a small change.

As already discussed, we might want to thrive to add more unit tests in the crates themself (where testing might be easier), instead of relying on external tests (in operators). It then might be possible to eliminate some of the manually implemented PartialEq implementations.