refactor(core): improve readability and robustness of FeedBackHandler

[joshtrichards]

• Resolves: #

Summary

• Fix/robustness: The progress reporting is now consistent: both advance/progress and finish messages use the same variable for total steps (there was a risk previously, albeit a small one, that the most recent would be reported as the total step denominator)
• Fix/robustness: Each message construction trims and safely defaults the description or message field so that empty values are handled gracefully.
• Readability: Each event type is now dispatched to a dedicated private handler method
• Readability: Variable names adjusted to make the intent of the variables much clearer
• Maintainability: More descriptive class-level and method comments help clarify intended use and logic.

Retains original behavior/business logic. Only potential user-facing output changes are the fix/robustness items noted above, which are only applicable in rare edge cases and are ultimately fixes for bugs.

TODO

• ...

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)