Fix metrics view annotation validation checking the metrics view's model/table instead of the annotation's

[nishantmonu51]

• The "must set exactly one of model/table" checks inside the annotations loop in parse_metrics_view.go read the metrics view's top-level model/table fields instead of the annotation's own fields.
• As a result, an annotation that set neither field passed validation and emitted a spec annotation with an empty name, model, and table; and annotations on parent-based derived metrics views were always rejected, since derived views cannot set a data source.
• Changed the checks to validate annotation.model/annotation.table, and added parser tests for both error cases plus annotations on a derived metrics view.

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!