Importer creates duplicate citizenship properties for same country with different time periods

Problem

The importer creates multiple citizenship properties for the same politician-country combination when Wikidata has multiple statements with different start/end time qualifiers. This results in 30 duplicate entries in our database.

Examples

• Edward Leung (Q22094633) - 2x China (Q148)
• Anne Hidalgo (Q2851133) - 2x Spain (Q29)
• George Weah (Q173139) - 2x France (Q142)
• Ricky Martin (Q128799) - 2x Puerto Rico (Q1183)

San Marino (Q238) is particularly affected with 7 politicians having duplicate citizenships.

Expected Behavior

We should only store one citizenship property per politician-country combination. The time period qualifiers (start/end dates) are not relevant for our use case.

Suggested Fix

During import, deduplicate citizenship statements by (politician_id, entity_id) - only import the first one encountered or the one without time qualifiers.

Start at the importer code that processes Wikidata citizenship statements and reproduce the duplicate cases listed in the issue. Ensure the import keeps one citizenship per politician-country pair regardless of time qualifiers, then verify that the affected examples no longer create duplicate database entries.