Is isSelfIssued being used?

Is that method of the `BlockSupportsMetric` class dead code? There is a comment on `BlockSupportsMetric` claiming its used in some metrics that SPOs find useful. But we don't see any uses of `isSelfIssued` in our code or in `cardano-node`.

Locate the BlockSupportsMetric class and its isSelfIssued method, then search the repository and cardano-node references mentioned in the issue. Determine whether the method has any callers and whether the comment about useful SPO metrics is supported; done means the method and comment have a clear, evidence-based status.

Written by the indexing model from the issue text.