Add EvaluationResult as rule evaluation result.

[blkt]

Summary

Return a structured result from the evaluation engine, as well as an error.

A followup PR will update each of the evaluation engines to return a useful structured result, currently it is left empty for the sake of making the PR easier to review.

Change Type

Mark the type of change your PR introduces:

• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

Unit tests were updated according to the change.

Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[coveralls]

coverage: 55.364% (+0.007%) from 55.357%
when pulling 8011c29 on feat/eval-engine-evaluation-result
into ee82c4b on main.