Add Enriched Citations API Endpoint

[dpieski]

Summary

• Add EnrichedCitationsClient for the USPTO Enriched Cited Reference Metadata API (v3), with search_citations(), get_fields(), and paginate_citations() methods
• Split BaseUSPTOClient.paginate_results() into two methods to support different pagination styles: paginate_results() for offset/limit (existing APIs) and paginate_solr_results() for start/rows (Solr-style APIs like Enriched Citations)

Details

• The Enriched Citations API uses Solr-style start/rows pagination keys instead of the offset/limit keys used by other USPTO APIs.

New models: EnrichedCitation, EnrichedCitationResponse, EnrichedCitationFieldsResponse.

In general, when a loop or global variable is intentionally unused, it should be given a conventional “unused” name (such as _ or a name containing unused) so that both humans and static analysis tools recognize it as deliberate. Otherwise, the unused variable should be removed.

Here, the loop on lines 114–116 iterates over client.paginate_citations(...) but never uses citation. The best fix without changing functionality is to rename the loop variable from citation to _, which signals it is intentionally unused while leaving the logic (incrementing count, enforcing max_items, and breaking) unchanged. No imports or additional definitions are needed, and no other parts of the file reference this particular loop variable, so the change is localized to the for statement in examples/enriched_citations_example.py.